i got a great idea for later Game may you should do something like stuff that appears suddenly and you can invest Money or Angels in it and then get a Item that Boost something that would be Great cause you can do a Market were Players can trade with others thats a littlebit in way towards multiplayer :) its only an idea hope my english isnt to bad sry for that :D
 "AdVenture Capitalist"){kind=icon}
 "Rush Team Free FPS Multiplayers"){kind=icon}