To allow Astropaths to participate in combat equally with some of the other characters, I've been contemplating adding a Penetration value equal to their WP bonus, or half that. This still seems weaker than most of the standard guns out there, not to mention the increased risks of using psychic powers.

It seems to me like some psychic abilities like Psychic Scream should potentially ignore armor.

I agree. I can't find it written, but 1d10+Psy is going to bounce off most things.

Is this another thingy for the errata?

in my game I allowed the Astro to ignore Armor since the powers name is Psycic scream hence targeting the targets mind.

And the Pre.rec for the power is Mind Probe so...=)