Unless you're doing track days, I think it's enough for the road. There's plenty of room for a massive turbo if you want though
I will admit that I felt underwhelmed, but only when I got back in the Clio and chucked that about on the drive home!
That's like saying there's no need for Porsches or Maserattis or anything remotely powerful on the road...
The mx5 is plenty powerful enough to enjoy at or below the speed limit, however, for me, the GT86, didn't seem to have that same feel.
I did test drive it after the mazda 6 mps and the 350z so probably why I felt a little underwhelmed.
You're right though, it has enough power to have fun in on the road - but for such a great looking, and specc'ed car, it's a shame they just didn't give it about 15% more power which is all it really needed to start making it a little bit more exciting.