We've bought then sold a few duplicate chips (most for about 1/2 of what we probably could have sold them for, trying to share the luck). We've sold 2-3 that I've posted just to show what we'd bought--and then received nice offers for 'em (but we've turned down more offers than we've accepted...depends on how attached we are to the chips ).

As for the best chips for investment purposes...a chip that's valued "S"-"Z" that's found in a cigar box for $5 is probably the best investment chip that you're going to find...