I LOVE the wheel. I'm using a Logitech Wingman FF, which is the exact equivalent of the GT Force wheel, except for no GT3 sticker in the centre and red handles instead of blue.
Main reason why I love it: infinitely more realistic race experience. There's just no comparing driving with the wheel and with the dualshock, especially when the wheel on Simulation mode. If you then put Sim tires under your ride, it's even better.
If you're very used to the DS2, it may take a little while before you drive faster with the wheel though and because the DS2 is a lot less realistic it allows for better times on some circuits. But on other circuits, the wheel is definitely the easier tool to get fast times with, and in general in the slower cars you'll also often do better with the wheel.
But I would never voluntarily go back to the DS2 - it's a kids toy, the wheel's a grown up thing.

The wheel has realistic spinouts

it has great force feedback, you can feel where the carbalance is (is it leaning left or right) and use that to judge your chicanes, you can feel the rumblestrip and the white tracklines, it's much easier to steer just a tiny bit or brake just a little, etc etc etc etc.
Me *love* wheel.
And the Wingman FF is only about 50 Euro's now, I highly recommend it (it's also the most compatible wheel, working with the most games, and the wheel GT3 was designed for).