Not That Many By Comparison
If I had the money, I would probably be in the everything camp. As it is, in the real world, for 3e I have PHB, DMG, MM, MM2, MotP, D&DG and SBG (my only softcover). For v3.5, I have Draconomicon, Frostburn and every Eberron hardcover there is. I also have every novel except Tales of the Last War, which strangely does not appear in my local stores. I don't have any of the adventures though. Maybe one day I'll get them, but the reality is that I would rather create my own for now. If they come out with a level 1-10+ adventure, I think there is a good probability I'd buy it.
Also, I don't collect miniatures. The only miniatures I have were a misguided but well intentioned gift from my parents from when they went on vacation last summer.