Although I've only been vaping for a bit over a year, I, too, have an ever-expanding collection. Nowadays I mostly stick to rebuildables, but even those are beginning to accumulate. There's only so many rigs I can keep in rotation and still stay sane - I'll try to pull something different out a few times a week, but there are a few things (like my Vivi Nova tanks) that just don't come off the shelf much.
Once I get a few things taken care of, I think I am going to take a hard look at my inventory and start PIF'ing a few things here and there.