I wouldn't be so quick to call it a big waste of money. From what I see on the news most of America is flooded at some point during the year. So, that $40 part could end up saving you $5000 for a new motor. I don't have active sonar on the front of my car to tell me how deep the puddle in front of me is. When it really rains hard, I get a 10" deep puddle covering the entire road in front of my house. Sure, I 'might' be ok without the bypass valve, but like MaxBoosT/StriderGS said...
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.