How many collectors?

I think that I read in one of the articles about VCF east that Sellam thought that there might be 500 serious collectors. I can't remember the exact quote but it was something like that. I was just curious to know if that number (whatever it was) is approximately correct? How do you define "serious collector?" Is it by number of machines a collector has? Would someone who has a handful of very rare computers qualify as serious? What if someone spent years doing an educated hunt for just one particular system that no one else has, and found it. Would they be a serious collector? Or is it based on the kind of computer being collected -like DEC vs. Apple, etc.? I'm interested in peoples opinions on this. Also, this post is NOT about Sellam's exact quote, it's about the idea behind it. Ernest