One way to balance /day effects of shaped items would indeed be to burn out the slots used for them. The idea of trading CL's for invocations where it hurts a caster most, and it's not as if the magus could not just have gotten a buff or used an item.

The servitor lets the magus use the more traditional in-the-back position and may stimulate her to learn buffs and help the party shine. Both would be a way to make sure that an at-will spellcaster is not outshining the rest of the team. I do not propose letting the servitors share the same abilities as when the magus is hit by a spell, so Lightning Rod would help her out to be targeted anyway. However, I must think about what happens if the servitor is destroyed. Maybe the material can simply be gathered but need a break to be reconstituted?