A fun variant is trying to score zero points without penalties. So no beaching boats on an island, leaving houses in the sea, etc. Not as easy as it sounds!
The only problem is you can't play boats because they always score at least 1 point in the sea. If it doesn't mess up the balance, a better rule for boats might be "1 pt for each square away ... minus 1 pt" like forests. Maybe with a bonus point for each square beyond say 5.