Will-

Looks like you've gotten a lot of responses, so i hope I'm not repeating something. But to answer your question of

"If I have to buy chips for $5-$10 bucks apiece (prices I've seen online), why not just buy the ones I want instead of buying a bunch of duplicates that may or may not be of interest to another trader??"

I'd offer the following:

If you're purchasing chips from sources other than casinos, and those are sources most of the world has the same access to that you do, I personally don't see any reason to purchase traders -- for exactly the reason you point out. I would venture to guess, however, that most chip collectors are also gamblers (at least to the extent that they ocassionally visit casinos). Since you can get chips at a casino for face value, it's worth picking up some extras. THere is certain to be someone who doesn't have access to that casino, who would like one of those chips. That person in turn trades you a chip he has easy access to. To me, that's the beauty of trading.

Hope that helps.