I'm thinking you all need to do something new and different. Perhaps you could make expansion sets for existing games, but I think you'd be better off making new "Tycoon" games. If you estabished yourself as the leader in PDA simulation, tycoon games, customers would to you for all their simulation wants.

I still like the idea I had many months ago of combining Plant and Fish Tycoons. Create aquatic plants for the tanks, use dead fish as fertilizer, etc.