This came up before but it was about how much you can get in, in a day. It was between 10-20 attractions.
Really if you hit the big/classic rides IMO that's, Space, Splash, Indy, JC,POTC, HM, BTMRR, PP, Dumbo, Carousel, Buzz, Nemo, Raiload, Autopia, Matthorn, teacups, IASW, RR and the monorail. That's 19 in DL. In DCA: Soarin, GRR, Screemin, TSM, MM, ToT, BL, Alladin, Monsters add upto 9.
Of course the night shows and parades can eat up a lot of time.