Should i build spell pen as a Lich?

[Matt [Reckless Boi]]

Title pretty much, I've been mostly using lich spells ever since i merged spellbooks with the occasional ray for sneak attacks ( I'm an Arcane Trickster ).

[Toadally Awesome]

The best lich spells bypass spell resistance and Deadly Magic is a great ability that does that on top of silencing, but if you care about any of your class spells that allow spell penetration, you can build it. Merged spellbook caster level plus dark rites should be enough for all non-boss enemies regardless.