My decision was easy. I had an overpriced AMG, overpriced S2000, appropriately priced 350z, and a great price on a Z4 3.0si.
I drove the Beemer first and no-showed on all the other appointments.
For me (I drive a Honda element which I've modded and tweaked as far as it can go), anything is a thrill to drive and the si has been amazing. I don't push it to the limit, and will always know that it has more power than I've used or need to use. The sport rims and red leather catch attention everywhere I go, and getting an M wouldn't have added anything to the things that are important to me. I drive slow so people can take a look as I drive by, and if you want to catch their attention early, drop a gear or two and spend a few extra cents on gas. The exhaust tone is very controllable.