I wouldn't mind having one of the original card paintings.
I was actively collecting back when Topps started unloading the original art in the early 2000's via their "Topps Vault" auctions on ebay. I remember their first or second piece of original art going for roughly a grand and all the ones after that started going for $500 to $1000 more. I was the runner up on a couple of different pieces of card art (color final for the front of the card so it is *the* grail piece when it comes to art as there are of course pencil and color roughs out there as well), but I never won one of the expensive series II art pieces they were selling. Too bad I didn't step up to the plate and pull the trigger back then as prices have quadrupled or more for original art so they're out of reach for me now as if I had 6k to spend on a collectible I'd buy the nicest Tron pin I could find

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I did wind up with an original piece of art though, but sadly it's for the reverse of a card. It's from a series 5 or 6 card IIRC and has Johnny One-Note (the character below) on the back of the card in a comic strip. I haven't found it yet digging through my collection room, but I'll bump my GPK thread when I find it.

Lastly, check out some of the original art offered by my favorite GPK artist, John Pound:
http://www.poundart.com/gpk/roughs/index.html