Well.. we got the bending part, the diving, the vibrato, cardriving sound and some effects i can't really describe(like Petrucci 'hitting' the whammy and the note shakes with the whammy..)..
Listen to some of Vai's stuff.. he's good using his whammy... U can make alot of tonal dynamic with the whammybar.. And, i bet the guitar wouldn't be that much cheaper without the whammy...

Btw. Playing with a whammy is totaly different from playing without one.. i've just started playing with whammy myself..