Try to improve the game by giving the player more than one life, and maybe also add a menu like in the previous chapter. You can also use the Breakout game as a test platform to check out the helper classes you implemented so far. For example, you could write a log message every time the player completes a level or destroys a block and then check out the log file.
The next chapter introduces the Input class to make it easier to catch all controller inputs. A nice improvement to the game would be to implement rumble support for gamepads like in the last chapter and also shake the screen or add simple explosion graphics when blocks get destroyed. The sky is the limit; if you really like arcade games there are many ways you can improve this game and make it much more fun.
Maybe you are more interested in the helper classes and have several of your own helper classes you would like to add and test using your new knowledge. Now is the time to do that. The next chapter focuses more on reusability; the chapters after that only talk about creating a 3D engine and you might forget about all the useful helper classes until you miss some feature. The good thing about helper classes is that it is easy to improve them all the time. They may become a little bit big like the StringHelper class, but you can always refactor them.
Anyway, have fun with XNA Breakout and relax for a while. Try to get to level 5 without cheating - it is not easy.