I'm fairly new to SC2, but have picked up pretty well and after losing all placement matches ended up in the bronze league. Shocker!  So now I'm stuck trying to bob my head above 500 and usually end up going on runs of 4-5 wins followed by a few losses to kill all of my gained points. I currently sit 3 games behind 500. I've got two friends playing one diamond and one gold and both are playing with me to give advice, watching builds and so on. I've also been watching alot of replays, day[9] and Husky to gather alot of info when i can't play (at work) and to try and absorb as much knowledge about the game as I can. So I feel I'm putting in the time and effort on trying to improve and there lies the problem.
 
Since I've been trying to put all of this info into practice I've been losing more due to early game all ins, and shenanigans. Now Day[9] does alot of talk about the mid game, and always plan. So if I wanna go 3 gate, colossus I dont need to start building starports. if i'm early expanding its probably a good idea to drop a forge/bunker/spine crawler to defend while i'm initially weak. You see where I'm going. Problem is I've usually been having to resort to cheap tactics on the spur of the moment to defend and turn the games around. 
 
Example:  Last game I played a zerg 10 pooled to mass zerglings while I was going for my expansion and had minimal defenses. I held of the charge losing two zealots and cleaning up with probes. I ended up getting my 4 gates out and just having enough resources to warp in stalkers/zealots as   zerglings are entering my base. I would retain maybe 1-2 units after each push as the zergling count increased each push until i finally had 5-6 units after one push and able to warp in another 5/6 (i had 6 gates at this point) and then start pushing myself. With 6 gates and a working expo he just couldnt overcome with zerglings and had wasted enough money continually pushing and teching hydras instead of say banelings/muta to combat the mass ground force.
 
Now you might read this and say. Cmon bronze leaguer. Thats a win. Shut up and carry on. My problem is this is indicative of alot of my games. I get rushed and end up scrapping it out with opening units and am never able to get to any semblance of a mid/end game. Now about every 5th game i get to an mid/end scenario and get trounced for not having faced alot of mid/end units, and then not being able to have a decent direction to go in. 
 
Do I continue to try and win on opening builds until i get to games where its required i have a mid/end or do I take my lumps knowing that I will be better in the end playing each game like there will be a conclusion beyond intro units?

Yes. 
 
People get 6 pooled in the GSL man, there isn't always gonna be a mid to late game. Cheese and early all ins get a little more sparse as you get into higher leagues (I think). 

Finding a friend to play with you where you both agree to go for a 20 minute long game would also help with your situation.  Training partners are generally pretty good to high in improving your play.

I have a few pointers that may help you out: 
 
-  Stop using 'builds', hopefully by now you know the counters to various units and you should be constantly scouting your opponent's base with a probe or observer to see what type of units he is building and then proceed to build units that will counter his army. 
 
- For your trouble that you have getting an army with more mid/late units. You shouldn't be trying to build things like Carriers or Colossus's just because they are the final tier of units. For example, if your opponent is building Hellions, you should build Stalkers. 
 
Hope this helps you.  

 
Example:  Last game I played a zerg 10 pooled to mass zerglings while I was going for my expansion and had minimal defenses. I held of the charge losing two zealots and cleaning up with probes. I ended up getting my 4 gates out and just having enough resources to warp in stalkers/zealots as   zerglings are entering my base. I would retain maybe 1-2 units after each push as the zergling count increased each push until i finally had 5-6 units after one push and able to warp in another 5/6 (i had 6 gates at this point) and then start pushing myself. With 6 gates and a working expo he just couldnt overcome with zerglings and had wasted enough money continually pushing and teching hydras instead of say banelings/muta to combat the mass ground force.  Now you might read this and say. Cmon bronze leaguer. Thats a win. Shut up and carry on. My problem is this is indicative of alot of my games. I get rushed and end up scrapping it out with opening units and am never able to get to any semblance of a mid/end game. Now about every 5th game i get to an mid/end scenario and get trounced for not having faced alot of mid/end units, and then not being able to have a decent direction to go in.    Do I continue to try and win on opening builds until i get to games where its required i have a mid/end or do I take my lumps knowing that I will be better in the end playing each game like there will be a conclusion beyond intro units? "

Scouting is key. While builds are great for a solid foundation for the game, you need to become more reactionary to counter whatever the other player is doing. If he is one basing then that means he is probably going to do some early push to try to win or something. If he fast expands that means he'll be weak early on but will have a stronger economy mid-game; you can abuse his FE by killing it off or harassing.

Watch Day9,he will help you.

" Scouting is key.