With update v1.3.4 you will get the ability to pause the game and build - before this was not possible. Now you can just pause the gameplay and build/upgrade your towers without risking too much.
Also (!) every new game starts paused, so you need to start it - use the flashing buttons in bottom left corner of the screen.
There were also some more speed improvements and some graphical goodies built in.
Unfortunately Amazon needs a whole load of adjustments made because they do not allow links to markets - so scoreloop fails, facebook fails etc - this version was built for amazon also, but it will need a bit of time until it is approved there (if it gets approved .. it's always a pity..)
Please, let me know, if you miss features, they may be subject of a future update ;-)