Wet weather doesn't in itself create a track bias. Wet weather MIGHT create track bias depending on the track. Rail position being moved and creating firmer going on the inside couple of alleys though would create a bias [biased toward the inside] as those alleys are now faster. This 'bias' [or punter perception of it] could and often does change during the day.

I never [seriously] bet on any track worse than 'good'. The punter has enough things working against him already without worrying about his runner having crap kicked up into it's mouth and face at galloping speed as well !!!