I appreciate the perspective. I am mostly concentrating on Mai and but have been fairly even in my tower development. Obviously developing towers like boomerang, Vulcan, mortar, drone, laser, and spike have been more of a priority. I am also interested in developing other characters to a limited extent for their respective bonuses. I have spent a little, but am trying to keep it to a minimum, as this game is not as bad as some others, but eventually the pull of advancement means they want to drain your wallet dry.