The game is certainly enjoyable, and I paid full price for it. $60 sounds expensive though. You should look around for a new copy lying around (that comes with both game and mat, for around $50).
That being said, if you are DDR veterans, you probably should invest in another DDR game, as Mario Mix is nothing difficulty-wise, compared to the stuff on other platforms and in the arcades.
But if you are just beginngers, then Mario Mix is a great game to start you off in the DDR world.