You could also dilute with a can of coconut milk and saute and puree some more vegetables (onions, red pepper, maybe a potato).

Id second the yoghurt thing, but rather than putting it in the big pot of curry etc, add it to each individual amount u dish out so you can judge it better, Or leave it to people at the table to add according to their own preference? You could say you made it like that too ;-)

Too much curry powder? Well you can't remove it so you have to add more of all the other ingredients. Or make another batch without the curry powder and combine the two. It might help to dilute the sauce with plain yogurt or cream.