[ArchonShiva]

Clerics using a $40 scroll heal more on average than a $120 potion; they aren't really getting their thunder stolen.

However, the penalties are mostly to prevent people from recovering ridiculously fast in more down-to-earth fantasy, as well as prevent repeated 1-point heals at zero FP cost due to skill.

Here's an alternative that will change how the game feels but won't break it: Repeated healing spells don't have a -3 penalty, but both caster and subject pay the FP cost, which cannot be reduced by high skill.

You could even let the caster choose which of the two rules they will use for each casting.

As an aside, you can recover unlimited HP for free with Stop Bleeding, Esoteric Medicine-15 and a very weak cutting or impaling weapon. Expect your GM to be upset, though.