You really don't need to spend HPs on followers to improve them since they
improve by themselves. Since their skills/keywords are based on the rating of
your best skill, as your best skill improves, so do they. Followers are just
that. The focus should be on the PCs.
OTOH, I liked the idea that someone suggested (sorry, I forget who) about
using a followers combat skill until enough APs have been lost that they drop
from the fight. This allows bodyguards to be bodyguards.
Camo