hrm i doubt it will make alot of difference in the wet aslong as you still have plenty of tread. when going to the track they make you put your tires up to about 42psi+ cos its safer.
as the guy from there said "you dont need to worry about excessive tyre pressure, the rim will buckle before the tyre pops"
i prefer to have more pressure than your "standard" car because it gives you less roll when cornering, and its safer at high speeds, the less pressure the more the sidewall flex's as you drive, which generates more heat so your more likley to get a blowout ect. i havent noticed any difference in the wet, i mean most of the tyre is in contact with the road anyway, all having it flatter will do is wear the edges more.