I like Grossman, and his numbers improved greatly at AA Altoona after a slow start. Owens and Cain have seemingly become soft-tossing lefthanders who have trouble missing bats. I do not believe the Pirates will suffer by losing them in a trade. Nevertheless, Rodriguez is a bit old and will remain a Pirate for the next few years. Pirates fans, of which I am one, can now only hope that Rodriguez and his salary do not absorb resources that would be better used elsewhere.
Huston, I believe may get a middle of the rotation starter in Owens and a decent leadoff hitter in Grossman. If the Astros achieve this with the Rodriguez trade I'd judge it a success for the Astros.
The Pirates, on the other hand, need to have Rodriguez help them get into the postseason this year if this trade is to be considered a success.