There's not doubt that "car wrecks" as you call them are fun to watch. Hell, I love a good slugfest as much as anyone else and fights such as Garcia vs. Korean Zombie are up there among my favourites. And I'd be lying if I said I wasn't cheering my ass off during Wandy's fight against Brian Stann.
Now, do I wish that GSP would open up a bit more at times and go for the kill? Sure. But at the same time I can certainly understand why he doesn't. Take for instance his admission that he could've taken Diaz' back, but chose not to. Let's say he did take Diaz' back, could he sub or finish him from there? Highly unlikely. Yet if he does take the back, it opens up reversals and scrambles for Diaz, and you really don't want to mess around with Diaz getting control on the ground. GSP probably worked out the risks & payoffs and decided it wasn't worth it. And I can't blame him for that.
Looking at the UFC, all the champions fight smart, and I don't think this is a coincidence. Some are more aggressive or flashy and take more chances, but all of them work towards their own strengths while shutting their opponents down.