Im in love with the new patch of the game but have some ideas:
new perk- when having multiple of the same item in your inventory, the power of the item increases. E.G if you have multiple UFOs they could shoot faster or multiple ice mine legs could be placed faster.
Could the hearts that the shopkeepers sells cap out at 3500/4000, because any more than that and it could take multiple wave sets. (I just don't want to have to play for 30+ waves just to get 1 heart.)
make rare items less common!