I've got a copy of Deadly Premonition ready to play, but after reading some of the hints that they were going to be starting the 2nd endurance run I'm considering just returning the game and watching the ER. Since both P4 and Deadly Premonition seem like story/dialogue dependent games, I was wondering if people who had already played P4 before watching the endurance run thought they might have enjoyed it more if they were going into it without any experience with the game.

That's probably one of the reasons why I won't watch the Endurance Run (besides the ridiculous length): because I know I'll play it someday, and I don't want it spoiled for me.

I enjoyed the Endurance Run much more because I knew what was coming.  Made me really excited to hear what Jeff and Vinny's reactions to my favorite scenes would be.
 
In fact, I played through the game a 2nd time just so I could refresh my memory on what was coming up.  I' d usually keep about an hour or so ahead of them in my 2nd play through for that reason.  
 
I plan on doing the same thing with Deadly Premonition.  Will probably start playing it Sunday just to get ahead of them.

I had already played through P4 before watching the ER and thoroughly enjoyed it. I don't know what is better though: to play the game beforehand or not.

I enjoyed the ER well enough despite having beaten the game before it started.  I didn't watch every last episode, though.

I watched the ER through in its entirety, then bought a PS2 and Persona 4 last year to play through myself. Didn't make me enjoy it any less.
Doing Social Links and battles your own way still feels fine on a second run, and the story elements of the game were never really spoiled, I just had two other guys in the room watching them with me and afterwards I did my own second playthrough solo.

Nah, I don't think so. I'm glad I got to play the game in its unfiltered form first. Watching the Endurance Run is a bit like watching a great movie with a commentary track over it. It's a cool new take on the whole thing, but if I hadn't played it first, I'd feel like I was missing out.

" Nah, I don't think so. I'm glad I got to play the game in its unfiltered form first. Watching the Endurance Run is a bit like watching a great movie with a commentary track over it. It's a cool new take on the whole thing, but if I hadn't played it first, I'd feel like I was missing out. "

Hell naw. I probably wouldn't have even watched if I hadn't played it yet. I wouldn't want them spoiling the game for me.

About a couple of weeks into the start of the ER, I saw a few episodes (about 4) and decided to stop watching because I immediately realized it was a game I wanted to play for myself, after playing through its predecessor.  I then resumed watching the Endurance Run and I enjoyed it very much as I knew what was coming and anticipated their reaction to it.  I also was a bit frustrated in some earlier parts when they made some idiotic decisions (but that soon stopped as that made for part of the charm of the ER).

I actually was playing them together.  I was maybe 10 hours into the game when I started watching the ER, so I'd leave the ER run on my computer while playing P4.  
 
They played off each other pretty well.

" That's probably one of the reasons why I won't watch the Endurance Run (besides the ridiculous length): because I know I'll play it someday, and I don't want it spoiled for me. "

" I enjoyed the Endurance Run much more because I knew what was coming.  Made me really excited to hear what Jeff and Vinny's reactions to my favorite scenes would be.

I watched about 60 or 70 episodes of the Endurance Run, then stopped to go buy the game and play it myself. I'm glad I watched as much as I did because I think it made the beginning of the game more enjoyable. 
 
Watching the Endurance Run does not make Persona 4 any less enjoyable. It's still one of the best games I've ever played.