Wow lots of responses, thanks guys!
I am one of many victims suffering from Steam Disease, the horrible affliction that causes your game library to swell 4 times the size of what you will ever actually have time to play due to all those bundles and sales they have...
I'm getting better... slowly...
I just noticed though that often when I go to consider a new game to play I will check the DLC for it first to see if I have ALL of it. I'm not overly concerned with extra "maps" or "costumes" or fluff items but if there's any story value at all to the DLC, yeah I'll want it!
Fallout New Vegas' DLC may at first glance be self-contained stories/areas but they also expand the main game's narrative AND add 20 extra levels to gain (5 per DLC), which does affect your native enjoyment of the game.
Skyrim perhaps a bit less so, I also hopped on Skyrim like a fat kid on cake when it came out but the additions of the DLC don't really cross over into the vanilla experience unless you let them (Alduin getting a crossbow to the face while Durnheviir torches his butt is a notable example for me

)
Civ V I got the Gods and Kings expansion but after reading what Brave New World added? No way I could play it now without the constant realization that I'm 30$ shy of a much more amazing and robust game.
I bought the Mass Effect Trilogy for PS3 and while it includes some DLC, it doesn't have all of it, which means I am taking my sweet time through playing ME1 since I know I won't want to jump into the second or third one without the full package.
Granted then there's games like Agarest: Generations of War which when I first saw it on Steam nearly had me rage out over the $97.71 pricetag of all it's DLC... until I realized every big of it is simply extra cheater-y items to make the game easier and add no true extra worthwhile content to the game... well that's the kind of DLC I can avoid without feeling like I've robbed myself an experience.