When casting remote attack spells...

[SlipperyJim]

Sorry, I wasn't clear. Mind Hunt definitely benefits from penetration bonii. I once whacked a Pretender with a Mind Hunt.

S2 mage + Rune Smasher (penetration) + Starshine Skullcap (+1S) + Ring of Sorcery (penetration and +1S) + Spell Focus (more penetration) = dead Lord of the Summer Plague

However, I'm not sure that Mind Hunt benefits from any additional levels in Astral magic beyond the S4 required to cast the spell. If I had to choose between Astral boosters and penetration items, I'd pick the penetration items.