So this is how I imagined the shop to be. My paint skills still rock. As you can see there are two tabs at the top, "Shop" is currently selected. At the other tab called "Your stuff" you can see your bought Upgrades/Hats and set your current hat. Bought Items will no longer show up in the Shop list. The other stuff is pretty self explaining, it's just an example of how it could look like, and I think I missed out something.