In theory lowering your car may affect wet-weather grip, but there are lots of other factors involved (tyres, tyre pressures, srings, dampers, anti-roll bars etc.).
One reason why race cars are set up softer in the wet than the dry is to do with weight transfer. For instance, on a right-hand corner you would want most of your weight over the l/h front wheel (this why you see kart racers trying to headbutt their front wheels in the wet).
By lowering your car you are lowering its centre of gravity, thereby reducing weight transfer.
However, on a FWD car this may actually help traction (less transfer to the rear).
Having said all that (and its not a very clear explanation) I would have thought you would have to lower the car by a lot to make a noticeable difference on the road.