I've been gaming for almost 18 years. I had ton of books...all of the Editions of D&D--except for the 1974 version. I had a bunch of modules, supplements, Dragon and Dungeon Magazine. I had a goodish collection of White Wolf stuff. I still have MERP/ROLEMASTER and WFHP. I have dice, miniatures, and terrain gallore.
And then one day, just a few months ago, I looked at my huge collection and thought
"Dear God, I've probably spent at least $8,000 on this "hobby"...and where has it gotten me?" The answers and thoughts to that question terrified me. Now, $8,000 over a period of 18 years equals about $444 a year. Which actually sounds about right!
What's worse is that I might be moving soon and move all of that "stuff."
That saying is right on: "The more stuff you own the more stuff ends up owning you."
So I've starting selling the stuff that I don't find cool or haven't used in years. The first stuff to go was a bunch of 3.0/3.5 third party books, followed by 3.0 "splat" books and even the 3.0 core rules. I kept asking myself "When will I use this?" If the answer was "probably not ever" then the item came up for sale.
This was soon followed by 2nd Edition books that I hadn't even glanced at in years: most of the "Complete" Series, some modules and the like.
And then went some of the non-D&D stuff: Vampire, Mage The Ascension, the old version of WHFP, and so on.
I made some "okay" money...better than what I've seen on ebay where huge lots of D&D books go for really cheap.
And you know what? I've discovered that I do not even miss this stuff. In fact, I've extended this philosophy to my book collection and other aspects of my life.