Saw Palmetto will affect erectile function, but that doesn't mean you won't get an erection -- unless you're prone to the problem.
But why are you taking SP for BPH caused by stimulents? SP reduces prostate hyperthrophy by reducing DHT, which is not the same cause, so the SP will probably do nothing.
Nettles and pygeum is a better choice. Not using all those CNSS is an even better choice -- not to mention they'll give you major "shrinkage." (And I don't mean of the prostate)