With Repair 1, you can use a Repair Hammer once, bringing it up to 20/100. The Hammer breaks.
With Repair 2, you can use a Repair Hammer twice, bringing it up to 20/100, and then again to 40/100. The Hammer breaks.
If you do it that way, then deciding which stuff to use the hammer on could be another choice the player has to make - do they restore 20 points to two things, or 40 points to one thing?
I see where you're going with this, but considering the scarcity of ability points and relative abundance of gold, you'd have to make repair hammers either really rare or extremely expensive (both of which situations would be pretty strange) for this to work.
Instead, something simple like having the Repair skill only fully/mostly repair "simple/tier 1" equipment while only minimally/not at all repairing "complex/tier 5" equipment at ability level 1, but at ability level 5, you could repair (and even improve upon) pretty much anything.
