To be honest, I don't think it matters what day you go to DTD. The crowds are pretty much the same every day. Remember it really is nothing more than a spread out shopping mall. It doesn't have attractions, to speak of, just retail shopping and dining and some entertainment, but during the day it isn't anything special.
I'd just choose what ever day you feel that you might need a break from the park and a little bit lower key existence. That's what I do. If my body needs a break but I still want to do something Disney, it's hello DTD.