Excess Cash - Exchange Items

To add another dimension to the game items you buy could be put in a sort of "wardrobe" in the base. Fully completed Items are technically bought so why have to sell them when you get to full build just to change to a different item. Example is when you have used the Guardians Angel. Why not hang it up and swap it for something else you have bought that serves more purpose as the game progresses but then bring it back once the cooldown has finished.

Another idea is adaptive item slots. Once you have 6 completed items another slot will open up for building. This allows build paths not yet explored.

Anyone want to add to this?