Heavy, light, etc. was just an option. Could be just like more armor types with different stats. Just so the game isn't so linear. I don't like the fact that everyone after level 16 looks the same (unless they have coin items) until he can get the next armor.
And for the shop button, it would be useful in full room. If you disconnect you risk not being able to come back or loosing your Room master (yeah, you can ask someone to hold the room for you, but that is unnecessary).