I have too many role playing games. I think I have about thirty-three, if you count different editions of D&D as different games (which I do). I have more than that if you count various free games I have downloaded such as Labyrinth Lord. I have more games than I will ever be able to play or run. In many cases, these games are redundant. For instance, different editions of D&D... multiple superhero games, two different Star Wars games, and more White Wolf than you can shake a clove cigarette at.
I'm not sure why I buy so many games. I know one of my big interests is to see how each different game handles mechanics. It is interesting to me to see the different tropes valued by different game designers. I also think that some part of me wants to write my own homebrew rules system someday, and by reading different systems, I get a sense of what I like in game mechanics. I also like seeing different takes on the same type of game... The Riddle of Steel is a totally different ballgame than Cyclopedic D&D, even though they are both "fantasy" games.
There has been some rotation on my old gaming shelf. New games come and I get rid of old ones, though the rotation has decreased as adult life has siphoned away some of the time and money I used to be able to invest in buying and reading gaming books.
I think, to an extent, I am also suffering from "new edition fatigue." In the last few years, I have seen just about every one of the "big" gaming companies toss out a new edition or reboot of some kind: D&D 4th edition, Shadowrun 4th edition, GURPS 4th Edition, the new World of Darkness and all of its new game lines, and so on. I've largely given up on buying source books or supplements of any kind, since roleplaying games seem to have settled into a cycle of obsolescence worthy of video game consoles.
System curiosity aside, how much mileage do I get out of any given game on my shelf? The answer would be "depressingly little" for most of them. In light of that, I don't think I'm going to be adding any more material to my gaming shelf, unless I can see myself using that material within several weeks of purchase. No more new systems, no more splatbooks. I think this is the year that I go completely DIY as far as pen-and-paper gaming is concerned.