The best bet for my library at this point is for fan-made material, to be honest. The entire suite of 3e was a huge chunk of change. 2e before it was a decent investment as well. As much as I love the Old World setting I won't be spending money on another edition. It's that simple, really. There are so many fantastic games out there that I want to run or play. I simply can't justify buying the same setting over and over again hoping that someone will get it right.
If a 4e comes out I'll gladly roll up a character and play it if someone else offers to buy it and run it, but from a GM/Collector standpoint I have to move on and be content with what I have. I doubt I'm alone in that regard.