How about we keep clams, but have a maximum of about 5? Could something like that work? Clams would be okay as long as people don't go crazy and build 20 of them or something. I don't know how you would police it, but you couldn't police a no-clam rule, either.
Ok, well, let's just go on an honor system that no one can build more than 5 clams I guess. Let's leave magic sites at default - that is still a lot of gems available I think. On a map of 154 provinces we might each expect to expand to hold about 19 provinces without any wars.
__________________
Algebraic geometry seems to have acquired the reputation of being esoteric, exclusive, and very abstract, with adherents who are secretly plotting to take over all the rest of mathematics. In one respect this Last point is accurate. --David Mumford