Well, the regular S2000 is just that, a regular S2000. (There's also a Type V in the game, which has a different steering set up, if you read the dealer descriptions). Both the Spoon and Mugen versions are modified somewhat. Once you get one, you can go to upgrade it and see some things have already been purchased. I have the Mugen (and regular S2000), which is good, but haven't gotten the Spoon.
The game also has a Spoon S2000 Race Car (which isn't all that great, I don't think), and an S2000 LM Race Car (which is superb; one of my fav).
They got pretty S2000 happy in this game.