I just got a logitech force feedback MOMO wheel for playing NFS:MW and I love it. I played the game for a little while with the game pad and it's soooo much better with the wheel. For one thing with the game pad it's kind of a pain in the a$$ having shifting, acceleration, breaking, and steering all on the game pad. It is way better having your acceleration and braking controlled by your feet, freeing up hands and fingers for other things. Having a shifter is really nice, and on the logitech momo wheel you have two paddles right behind the steering wheel so when your hand is on the wheel, your fingers are right there to trigger them (I have mine set up for nitro on the left and hand brake on the right though I never really use the hand brake).
If you enjoy driving games and play them a lot a wheel is a must have. If you rarely play them then maybe it's not worth the money.