If you have weekly lineups, I think an IP limit is not wise. There are plenty of times when a pitcher has 2 starts where the first one's a tough matchup and the 2nd one is at Petco- an IP limit means you often won't start that guy. And that's no fun
Enforcing legal lineups is the way to go. It's how my weekly H2H points league runs, and it's fine. You still have the "2 start pitcher streaming" nut to crack, but if everyone knows about it I don't think it's so tough. If you limit add/drops to certain days or use FAAB, you reduce the ability of a single manager to sit on the wire and stream 2-starters every week.