Ha, great question, rachylou!
I have trouble purging costume jewelry, and even though my excuse also is that it doesn't take up much room, at present I think I have too much that is unworn and likely not to be worn. It's a little like cami's and tanks--I worry that as soon as I toss one, I'll need just that color or neckline or something.
I'm trying to develop some criteria--questions--would I buy that today or something almost like it? Are there any annoying things about it that I forget until I wear it? Do I put it on and then take it off every time before leaving the house? Do I need to get a few nicer pieces, even "real" jewelry that will sub for many junkier items? I'm hoping these will help me let go of some.
I also have a clip-on earring purge crisis--I used to wear them because they were a good focal point, and well, I just did not have pierced ears and don't plan to. None are expensive or "real" jewelry, but I had collected many pairs to go with all sorts of outfits.
Then after awhile they just looked wrong. There might be a half-dozen pairs or so that have very minmal clips, or magnetic, and so look (almost) like the real deal.
I'm trying to get up the nerve for the big purge. Maybe save 10 faves or something as a safety blanket.