There is a scene selection button at the menu so you can start at anytime and skip the intro when you go down the elevator and jump start into the game.
I have already unlocked everything on ninjakiwi and i think there should be a login button so users can get the towers without having to level all the way up again.
 "Theme Hotel"){kind=icon}
 "Grey"){kind=icon}
 "Neverending Light"){kind=icon}
 "Johnny Rocketfingers 2"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}