ok I see no problem with building a stash of thread. Think about this. Back in 1998 I started sewing for lots of kids in the 4H clubs and of course they all needed differant colors so thread had to be bought. When 1 spool was needed I would buy 2, this continued throught the years. So the thread you buy now is 4 times the amount I paid for it back then.
Another point is, my son's girls freind is now wanting to sew but can't afford a lot of the supplies, so I just point her to my stashes and let her pick what she needs.
She's happy, I happy to have been able to share it with her.
Morale of this story, you can never have to much of any sewing supplies.