If you were going to give them yield, I agree give it only to the dwarves.
I would make it very low yield, like 1 hammer, and not increase. To make up for this, greatly increase to chance that the worked peak would give a resource that would increase the yield and automatically be hooked up.
I think this most represents the realities of mountain mining. A lot of the time, you could put in huge resources for no or little gain. But, the potential for finding good things may be higher.
In this case, the dwarves would be working a tile at a loss compared to a specialist, knowing that down the road it will be a big gain.
Another option would be to have the peaks tied into to Khazad world spell. In addition to raising hills and giving gold and whatever else it does now, it also gives all mountains in their cultural borders something like "not unpassable to units with dwarven promotion."
Then, dwarves could walk across them, mine them if worker code were changed a bit, perhaps even build cities on them (although the cities would be close to other ones, as they would have to be within the cultural borders anyway.