It is interesting how the driving experience of the two cars is perceived. I agree, I get more smiles from driving my Boxster than I would say I do in the 330ci. But I can't really say why. Is it because the Boxster is lower, the more nimble feel? Has BMW just smoothed off the rough edges of the 330ci to where you don't notice them while the Boxster is more raw? The 330ci has the same basic chassis other e46s, with a little more powerful engine and larger brakes.
I was a little surprised by the performance specs of the two. The 330ci is quicker to 60 than either a 2.5 or 2.7 boxster. 5.9sec vs 6.5 for the 2.7 Boxster. And the skid pad data is close, .89g for the BMW and .92g for the Boxster. The 330ci is 450lb heavier. I wonder how they might compare on various road courses? Would the Boxster win regardless or would the BMW prevail on less twisty tracks?
Comparing an S to an M3 is probably not quite fair as the M3 has almost 25% more HP at 333. I am curious if driving an M3 offers the same smiles as a Boxster?
I consider the 330ci coupe to be a "sporty" car. Much as I do a Mustang, Camaro, RX8..... It looks good, is reasonably powerful and has great handling. But, to each his own.