How can I handicap in Suburbia?
Generally, score handicaps are the way to go. You don't have to worry about playing games and experimenting in order to find a balance, you can just use the knowledge you already have of how much you tend to win by.

Money handicap could possibly work, but I think it'd be pretty tough - you only have so much room to adjust before it basically becomes a "you have waste one early turn to build a lake right away" handicap.

That said, you can also just not make the handicap formal: try to do the best you can every game, and accept the fact that you're striving for a larger margin of victory instead of worrying about winning.