This is part of the reason I mainly only collect games I've actually completed before or really really liked when they didn't have definite endings. Shaving off thousands of games from my want list makes spending the money I have to to get what I want later on down the road a bit less scary. I want games I collect to mean something to me, not just take up some space. Generally if I beat something once, I will want to play it again. There's never been a time where that hasn't been true.
I'm starting to miss some of the systems I had for a long time but sold and I enjoyed plenty of arcade type games on pre-NES systems to make me want to buy them again too. I just got an Atari 2600 again, and I'm missing a lot of common games I could probably find for $2 or $3 each somewhere.
Looking at my completion list from last year and this year so far, I think it's going to take a lot of time and money to even get caught up with my current want list. I mean that's up to 132 games and I don't have all that many yet and only few are CIB yet. I collect a loose copy and a CIB copy.
There are some games though that just cost way too much loose (Bucky O 'Hare for NES is a good example) where I might just want to buy the more expensive CIB copy and just call it a day on that title. I'm sure it'll be a nightmare when I finally get around to playing through Dragon Warrior III and Dragon Warrior IV. Of course if I play my cards right I'll have enough money saved by then to not flinch at its probably insane price.