Well, I've scraped my way into Diamond. About 180~ games later, my Platinum placed butt has moved from the top 10 position into the top 40 in Diamond. Luckily, or sadly, I've retained a lot of my points and so I entered Diamond around 1000 points in. I've tried to play more games and stay on top of this new league, but I feel it'd getting quite tedious. 
 

Terran vs Zerg

Terran vs Protoss

Terran vs Terran

Well, I've scraped my way into Diamond. About 180~ games later, my Platinum placed butt has moved from the top 10 position into the top 40 in Diamond. Luckily, or sadly, I've retained a lot of my points and so I entered Diamond around 1000 points in. I've tried to play more games and stay on top of this new league, but I feel it'd getting quite tedious. 
 

Terran vs Zerg

Terran vs Protoss

Terran vs Terran

Your conclusions sound pretty logical to me. Now, my advice may not be the best if you want to stay in Diamond, but here I go:
 
Against Zerg, I'd encourage you to try some more Ghosts. What I find is that massing Mutalisks is easy because they move so fast and heal automatically, meaning they can be used for constant harass  and escape before a single mutalisk dies. With some mass sniping action, you can get a kill or two faster than the Mutalisks can escape, forcing the player to choose between muta harassment and muta massing, instead of both at once.
 
Against Protoss.... I don't really have much. If every Protoss is going to go the same build, you're going to have to respond pretty much the same way every time. Random thought: Marines + Banshee/Ghost?
 
Finally, against Terran, I'd like to see someone mess around with Reapers for some late-game harassment and flanking against seige tanks/Marines. The way I see it, mass viking usually shuts down late game harassment (read: drops), or slows it down enough for the slow tank army to arrive. Reapers are significantly less vulnerable to this. Also, with the tank damage reduction vs light, I think speed Reapers just might be able to reach point blank range and snipe tanks/cut down marines.

I know that as a Protoss player, I get a lot more comfortable once it gets to the later stages of the game when Colossi and High Templar hit the field. Before then, and for that matter before I get a Robotics Facility down to do some scouting, I tend to be a little worried about the number of viable openings that a Terran player has. Marine/Banshee/Raven, Marine/Tank/Raven, Marine/Thor with SCVs for repair, etc. The opening I'm probably most comfortable defending against, oddly enough, is a pure bio push early in the game (2/3 rax). While I certainly wish the match-ups would open up from what they are now, I think it's going to be quite some time before that happens. I mean, look at how long Brood War has been out: I'm sure the builds that we see nowadays were never even thought of back in the early days of the game.
 
I can't offer much of an opinion on TvZ or TvT as much since I tend to only play T in team or custom games with friends. But if I'm on and you want to play some games to practice your TvP, hit me up. I'd be more than happy to spar with ya.

Just hit diamond too along with a wall. Can't beat early pvt and pvz with a roach rush kills me.

I've always felt TvZ was the hardest matchup for me, no matter how much people whined about reapers being imba or whatever (fun fact, making 5rax reaper a viable strat demanded some sick ass multitasking...). I'm pretty much in the same situation as you are, I can't handle the mobility and flexibilty of Zerg in the later stages of the game and with the recent nerf to the strong early game opportunities of Terran it has gotten much worse. 
If you go MMM both the Marines and even the Medivacs get owned by Banelings. You either stand there trying to gun them down (which will most likely will fail if he has more than 5 of those rolling little fuckers) or you try to kite which then kinda counters Medivacs since they can't heal while moving (no, I don't want them to heal while moving) and then Lings/Roaches/Mutas/Whatever deal the damage to your running army. I won't even think about Fungal Growth or I'll start to cry. 
If you go for a Mech build on the other hand your just slow and Vikings fail utterly. You either have to invest a huge load of minerals into Turrets or you have to park Thors all around the freakin map to deal with the inevitable Muta harass. At least the Tanks tend to deal with the Ground forces pretty nicely in that situation... As long as the Zerg doesn't go crazy with Nydus Worms all over the place. Slow Mech is slow. 
 
Best way so far has been a mix of MMM+Tanks+Thors. But going allround sometimes leads to not having enough of one unit which the Zerg can abuse by completely Tech switching in a matter of seconds... 
 
I suspect that the Raven could possibly be the key to the problem, the Seeker Missile seems heavily underused and I feel nobody has actually used it to it's full potential yet... 
 
 
TvP has probably always been my favourite matchup, but it's gone downhill for me as people seem to figure out how to survive the early game. You have some windows of opportunity open in the early stages of the game, Marine+Banshee+Raven pushes can end the game instantly in some cases, simple 3rax stim timing pushes can lead be succesfull too. But again, as the clock ticks it's getting harder and harder since the Protoss still progresses and as Terran your pretty much stepping on the same spot, you're basically stuck with MMM the whole game and as soon as both Colossi and Storm are ready for the Protoss you're just trying to slalom your way through their massive splash damage. 
 
Looking back at Blizzcon though I have hopes that it will get better in future patches David Kim said that the feedback they get about this matchup varies quite a bit. 
->  David Kim Interview 
 
 
TvT... yeah... I don't know. It can produce some really epic matches to watch (TLO v Hyperdub @ GSL#1, DeMusliM v Maka @ Blizzcon) but it is so! fucking! exhausting! 
Most of the time I try some Bio heavy timing push or Banshee rush to end the game asap since I don't want it to end in some WW1-esque besieging of the Siege Tanks...

Well I fucked my placement matches, so I gave up.

I ran a few trials of Ghost vs Zerg, and I think I've managed to smooth it out some. First off, it seemed to work better to go Marauder/Ghost than Marine/Ghost, because the Marauders do a better job soaking up damage to let the Ghost get it's snipes off, resulting in a stronger general-purpose army, if a bit weaker against mass mutalisk (though that's not really possible this early anyways). Most importantly, this shuts down the Roach attack I would be worried about with Marine/Ghost. Also, it lets you make continuous use of the tech lab you built for the Ghost. I figured the only major vulnurability of this army was speedlings, so I built a factory which let me make a few hellions and  a nuke. After that I timed a push with the nuke, which seemed to work well. If the Zerg leaves their choke to attack, you can run the aforementioned hellions in for some harass. If not, you can nuke their choke and the Zerg is basically trapped (extra trapped because the nuke kills their forward creep tumors). I found it easiest to expand around now.
 
For the transition, the smoothest one I found was switching the factory for a barracks tech lab and building either Tanks (if they go Hydralisk against your Marauders) or Thors (If they do in fact go mass Mutalisk, and you want to supplement your ghosts), and maybe some marines from that barracks. Finally, build a starport, and make some medivacs to boost your largely bio army and give you the Thor drop option or sight for your tanks. If you want, you can have that newly de-tech-labbed barracks build a reactor for your starport to land on, speeding medivac production if your army's taken a beating.

You should study up on some of the modern TvZ build orders Wunder, hardly anyone goes 1/1/1 these days. It's sorta been figured out. Zerg's are much better at defending all the silliness that can be done by a 1/1/1. Viking openings really don't do anything, banshees get less and less effective as zerg's deal with them more and more, stuff like hellion drops have become less effective with the roach buff and just zergs growing experience against them.  Most of the people I practice with, and play against on the ladder are opting for faster expansions, like 1fact cc, or even 14cc.
 
You should mess around with some pre-medic timing attacks. Check out idra's game vs qxc on metalopolis if you are curious about that. Those kinds of builds are a fucking nightmare for me if I'm opening mutas.
 
And as for how to beat mutalingbling, lots and lots of marines/medics with tanks with good micro. You need to stim the marines and run them away from the blings, stopping to get damage in whenever you can. It's really important not get your marines fungaled or surrounded. The tanks job is almost entirely to destroy the blings and let the marines shred the leftover muta/ling.

" @sixghost: I've tried to read up on workable TvZ strats but there hasn't been anything definitive out yet and a lot of people still open Reactor Hellion into Expand. I've been experimenting with 1rax FEs or Siege Tank expand and those have been working out decently for me. I'm trying to get a decent bio push off 2base to try and snipe a queen/force lings but I can't really get the timing down. When's the fastest time you can get Spire? By fastest I mean in a normal game, not specifically rushing for Lair then Spire. 
 
@StarvingGamer: Hmm, I usually play after a day[9] daily which is around 11/12am SGT and I'll probably get in another session around 9-10pm too for a couple hours. "