I think GP munitions should do, perhaps 50% damage, not 0%.
One problem is that lancasters could carry armour piercing bombs. That enormous bomb not modeled yet in AH was armour piercing (12,000lbs?). Also, it was used against ships (Tirpitz). Your solution wouldn't really fix the dive bombing lancs problem, I think they would dive bomb anyways.
Anyways, I really like that Kamakazi idea. I don't think they should be perked though, atleast not very high. A slow zero with no guns and loaded with bombs is an easy target.