How much Online Multiplayer is enough?

The mainline should never have a multiplayer component, because it would most likely come with restrictions even for offline single players and also siphon development money from the single player features.

However, if they made a spinoff that is only multiplayer (Sims Online 2 (or already 3?)), then this would be my prefered option. EAch player controls one neighborhood in a giant metropolis. We set out own local laws, festivals and souveniers that other players visiting us can enjoy. For souveniers I think at the very least a postcard collection that keeps growing with each player we visit.