Well I gotta say I don't think any threaded valve is as good as a solvent weld. I rarely reuse a pvc threaded valve after its been used once before. The pvc misforms when you thread something into it. I don't trust them not to crack on the second go round.
In addition the male adapter is the weakest fitting made. I suppose you could use nipples though.
Good point, I've had the same problem with threads. Don't tell anyone, but I have, in a emergency, glued the m.p.t. adapter into the valve and had it work.