Most of the information I have indicates that burning off crankcase vapors with a PCV is better than keeping it in the crankcase because it can contaminate your
oil fairly quickly. I guess that's not a problem if you change your
oil every race but in a street car if you want to keep your
oil for 2-3k miles, it's a factor.
Also, to me, keeping negative pressure in your crankcase seems like a good thing for seals and gaskets.
I agree with what Brent said about problems with the wrong sized valves or ones that for some reason don't work. That is why I went with the adjustable ME Wagner one.