If it had a nice new feature I'd spend that much easy. I don't see anything compelling on that MS mouse, though. My Logitech "laser" mouse seems to work on a lot more surfaces than other mice, so I consider that feature high up there. I also have like 8 assignable buttons which I consider invaluable. Having buttons for copy, paste, close tab, close window, etc. speeds up work considerably (horizontal scrolling is useless, though, so I always remap those first).
Wireless I consider a minus, though. When I travel I have to take the charger, receiver, and mouse instead of just a mouse. You also have to keep the stupid thing charged. Every wireless mouse I've had has used lots of processor time as well. All to get rid of a little wire that never bothered me anyway.