I don't think a single point of DR is all that imbalancing, but we have a "rare" treasury which only has a 1% chance of spawning its items, so it can always be moved there if it's too powerful.
As for being immune to rust monsters, we do plan on updating the scripts rust monsters and oozes use to not affect certain material types (wood, bronze, etc.) but it requires adding the material property to all existing items, which will take a while. The good news is that I've already done this for all loot items. There are still stores and NPC items to pick through, however.