How much can you learn from absurdly long TvT?

I realize that the endgame is an important aspect of the game. Setting up expansions, limiting enemy expansions, getting all those upgrades, etc. those things are all interesting to me, and are essential to being good at the game. After I've gotten all the upgrades and all that, and the game turns into positional tank warfare for half an hour, I start losing interest. The slightest tilt in the enemies favor will usually have me ending the game to just get it over with.

QUESTION: Do the benefits of riding out the uber-long games outweigh the benefits of quitting perhaps a bit prematurely and starting a new game? Besides managing expansions and position, is there anything I can actively take from this mess? 

Usually the entire positional warfare is defined by 1 or 2 key moments when one player messes up position for a split second, or a drop that hollows out someones main. Not much to be taken out of that, as opposed to learning more about the mid game/beginning of end game.

Maybe you guys can inspire me. =D