Does it help the companion to upgrade its power armor head with targeting?

For example the stealth doesn't seem to work on companion power armor, but tesla coils do.

good point.

I know better DR is worth it, but as far as the goodies go, not sure it is worth it. I usually just go for high DR and colorful paint for my companions.

If the extra goodies are only something the player character can use, like VATS enhancers, they're useless on NPCs. Otherwise, they should work just fine.

I've wondered the same thing, and honestly I doubt that things like the recon sensors and such make a difference for companions. I've never seen a companion use a jet pack or any of the other torso mods, so I have my doubts. I just build it the way I want it though. I don't necessarily have power armor specifically for my companions. I just have a number of suits that I switch between, so they all get fully modded regardless.