"Buy the Speedster, it is a different experience rather than driving around in the same old sedans". Pretty much sums it up, but since there are so few of either tearing around, you'll get lots of attention whichever way you go.
I would love a coupe, because in New England they just make so much sense, plus....my lovely wife has severe Glaucoma and cannot take the wind buffeting her eyes. We've got a pair of eye-gasketed sunglasses for her that work great and actually look pretty cool, but she still doesn't ride in my Speedster very much. Another thing to consider is that most of the "sport" exhaust systems available now for Speedsters tend to be bit loud, so the noise in the cabin will be higher than a Speedster, although the Speedster has more wind noise. Added to that is a bit more intake (carburetor) noise, because none of us have intake plenums which cut down the intake noise.
The last thing to consider (at least from me) is that, while the coupe windows are slightly larger than in a Speedster, you're still looking out through the windows of a small car. Whenever I've been in a coupe I always miss not having a top down.