Whammy pedal vs Floyd Rose? I don't think you can make a versus comparison here because the tone from a Whammy pedal doesn't sound anywhere near as natural the sound you get from a FR.
If you are a Satch fan, listen to his song "Searching" in which he uses a Digitech Whammy pedal (in +2 octaves mode i guess). You should notice that the tone is quite digital sounding. A guitars natural tone sounds thick and rich due to a large number of overtones present in it. However, a digital processor like the whammy pedal can track only a limited number of notes and hence only the most dominant overtones get shifted, making the tone sound like a set of beepers from old computers.
Satriani doesn't use a lot of whammy bar compared to someone like Vai, so a lot of his stuff should be playable even without one. He does that squealie + dive thing in a lot of songs though (like in Extremist). Just innovate and fill in the areas where those tricks come in. If you think you can cover a lot of them pretty accurately and that its just the instrument that is limiting you (only the tricks) its time to get a good FR bridge.
-- My current rig
Guitar: '98 MIJ Ibanez RG520 QS w EMG 81/60
Amp: Laney LC15R Tube, Fernandes 20W SS
Pedals: MI Audio Tube Zone Overdrive, Boss OD3, CS3, MT2, HM2, DS2, CE5, DD7, TU3, Beta Aivin DD2 Delay, Dunlop Crybaby 95Q, Stranger Vol Pedal, BBE SupaCharger
Others: Yamaha RBX 374 Bass, Yamaha MM-6 Synth, M-Audio Fast Track, Shure SM-57, Heet Sound E-Bow Plus
Wanted(pm if selling): EB VPJr/Boss FV500L,Ibanez w Original/Lo-Pro Edge