Seems to me that increasing ram command points would be the most logical solution here without affecting their strength too much. Rams (and catapults, for that matter), were never meant to be units that you send in droves of 10 or 15. Increasing their point costs to 40 or 60 would mean that you'd actually have to think about how many siege weapons and how many field units you want in your army, whereas currently you can get six rams for the point cost of two Gondor soldier bataillons.