I think we are misunderstanding each other. By DLC, I mean songs that you have to purchase and download to play on the game. Seems like you're talking about unlockables in the game.
IMHO While having access to all the outfits and instruments is fun, honestly who really pays attention to them? I certainly don't. My view is mostly focused on the raceway and the falling notes. If anything, if I had the option to turn off the character models and have only animated scrolling backgrounds like on Wii's all Instrument Mode without having to put up with the scrolling lyrics, I'd gladly do that.