It all depends on the area your in, if you think there is any chance your going to get water up near the fender well then you had probably better play it safe and get the bypass valve.

Yes the bypass valve reduces some noise, and that's not really bad, well in my oppinion anyway. I personally feel alot safer with it around here because it rains a whole lot. It does cost you a few horses but nothing major.

Once again, just consider the area you live in and go from there, it's not a bad investment.