I was given a sack full of thread that was from a quilt store that closed years ago...some of the spools still have the price on the end ...$ .15 for some, some were expensive, $ .35. I'm saving them but was wondering how one would know the value of a spool? Several have talked about how expensive the wood spools are, what makes them expensive (besides age) and where can I find out about them? Thank you.