I really like Jeff's idea of a challenge box or two. What I usually do with flies that I thought would work, but for some off reason don't, or just flies that I thought would be fun to tie, is give them away on the "For Sale" board. You could always donate them to a youth group, pass them off to a newby you meet streamside, etc.

Yup, I have started over many times in the last 40+ years of tying. I am presently fishing flies that were originated over 100 years ago. They still work very well, are easy to tie, and don't use a lot of expensive materials. I have added a few modern flymphs to that assortment and do quit well on the catching department.