I usually just repaired when the warning symbol showed up, unless I happened to notice low durabilities while trading, etc.
Repairing items does make them worth more. I put a couple skill points into Repair, found a couple items with a Repair bonus and bought another. All loot without full durability I stored in a chest to be mass repaired and sold off later.
Well by the time of divinity i had so many spare points left over, i just maxed repair and did all my own repairs..at 60% some melee fights can remove your sword from your hand at the wrong moment...i agree with getting a special suit put together for just repairing and this follows for casting certain spells..
Repairing at warning symbol can be too late.. but it comes down to individual ideals i guess. I prefer to max it out then i can spend more time killing and less time repairing.. tho i have to say, once i got flash attack at 30 i think the only item i ever had to repair was my sword..