Driving a 320d I would say that the likely thing I would like from a 325/330d is less of a diesel sound. I haven't had a chance to compare them closely but I understand the 325/330d sounds much better at idle.
Otherwise I find the 320d very fun to drive and anything more would get me in trouble (although I think the 320d eventually will anyways).
Currently I'm getting 10 litres to 100 km in city traffic (177HP)
2008 metalic black 320d coupe, black dakota leather, sport suspension, piano trim, i-drive professional, PDC front/rear, prologic 7, 6FL, heated seats, full electric sport seats, comfort access, folding mirrors, adaptive headlights, bluetooth, 189 wheels