The decision for FI is the right one. Although the M3 is capable, it's hard to call it a "fast" car when stock, or even modified NA - yes, 40hp *is* insignificant IMO (flame suit on).
I know, I know, I've heard it before: "it's build for the track" - "what are you doing pushing the pedal past 75% on the street anyways?".
But the truth is, even slightly modified 135's, Evo's, STI's & Genesi (?) run a stock M3. AMGs will eat it up. At least with the supercharger you are in the hunt. Once you get to the track, watch out, now you are able to set your sights on the P and F cars.
As for drivability - I think this is the BEST thing about SCing the M3. It remains *stock*. Aside from a grumble from the exhaust and whine/psssh from the supercharger, the car drives like it came from the factory floor. This is truly amazing. Daily driving is no problem at all, as their is little to no sacrifice on the luxury aspect of the car.
The *real* challenge supercharged M3s face is in the battle for traction. Even with 295s, 1st gear is useless and 2nd gear won't be much better. 3rd gear is even sketchy at times. This is why I always chuckle at the arguments over 20/30 hp in this kit vs that kit. Regardless of what power it's making, it's damn near impossible to get it down. That said, I will always opt for more power - VF620, ESS VT625, AA Stage2, Gintani Stage2 are all on the same level IMO.
Anyhow, the good news is - buying a kit used IS going to save to a ton of money. Even better, as more 2nd, 3rd, 4th hand owners come into the M3 they will be more willing to modifiy their cars and the demand for SCs will stay constant. We're currently in a 'transition' period right now with the M3 as it moves from 1st/2nd owners and lease returns to the "next generation". Thus the reason sooo many aftermarket parts are for sale. I'm sure many are unloading in preparation for the F30, others simply moving on. Not to sounds like a used car salesman, but "now is the time to buy".