City tile "growth"

It bugs me a little that city tiles are so weak --as a city develops, they usually become one of the weakest tiles. (Somewhat less so with P/H or P/H/bonus).

Is there a mod that allows city tiles to gradually beome more lucrative with tech or with overall city development?

If there isn't, can anyone tell me whether I can mod to allow, say, Replaceable Parts to add +1H, etc.? (My XML skill level is that I know how to use Wordpad.)

Thanks in advance.

It's not a bad idea, but I always sort of thought that specialists sort of represented the development of the urban city tile...