I'm not sure the gold for founding a city and free lighthouse should be on the same civ. They are both really cool effects, but when you pair them together it gets out of hand really quickly. If there is a design issue (not saying there is, but if there is one), I think it lies here.
The gold on founding fits with the myth of Carthages founding. I've been thinking about this, probably too much, and maybe keep lighthouses and just get gold on founding the capital and no other cities. Or, gain current sum on founding capital and when founding other cities, gain enough to invest in a shrine or monument type building. If this is possible to code.