Ninjaed by Stabbey! In addition to scrapping the whole concept of permanent max durability reduction, I guess I'd like any repair system to ensure:
1) There's no unrealistic equipment durability/quality "threshold" such that with a particular piece of equipment at a certain ability level, under the threshold you can do nothing, but above the threshold you can do anything. 2) Beyond the gold savings of not having to ask a merchant to repair equipment for you, there should also be a nice little "extra" for investing in the skill (e.g. the ability to slightly enhance equipment above 100% at level 5).