Voting no on exp penalty.

How about SE just make it incredibly difficult to repair items. We get the same amount of dmg to our gear, but no NPC can repair it... AND, switch back to specific items needed to repair specific armor/weapons. Basic items like crafted gear etc can still use dark matter, but if you say want a pair of "fists of the sixth sun" repaired, YOU would need to go back to the source (Cactuar Jack) or similar mob, and gather the repair item. Key item perhaps, so it doesn't take inventory, after which u have to go to a crafter, and bring up a trade window with your item, plus key item required to repair (plus potential reward).
That way, if your helping out some friends, and have a high chance of dying, maybe you won't equip your relic weapon...
So your weaker when your fearful, but when the going gets tough, you'll put a bit of extra work on the line to down Leviathan/Carbuncle/Whoever rocks up lol