I considered this and chose against it. Showing this is incredibly messy. If the user wants to send then they have to mess around trying to figure out how to make up 72 with the coins they have, it's just not good UX. Users can have a lot of different "coins" and peoples fingers are fat, the buttons need to be small. It's just not good experience. Two buttons is way better, if the user trusts they wallet they should trust it to tell them what they can and can't do.