These are good points.
The other car is my wife's MB E350 coupe, and my Cayenne Turbo S. So we already have plenty of practicality - I figure for variety's sake the third car can been a two seater. If I went for an M3 coupe, we'd have two 2-door, four-seat, roughly-same-size, modern German coupes.
I'd like a 911, but the price point is substantially higher. Cayman is in the price range, but I'm not that enthralled in it as a street car, and it doesn't have this crazy lease residual. Evora smells like a model rocket. Hence Z4.