Put abilities in the treasure chests.
Hide those randomly in the 2nd half of each dungeon.
This would make EVERY treasure chest in the game very exciting, because this gives every treasure chest the potential to be something amazing, by tapping into a gambler mentality of a potentially huge payout.

Money could be used to buy pictures.
But I think I prefer puzzle pieces because the challenge of putting the pictures together is more fun than simply buying them.
What if you could both find and buy puzzle pieces?  Choose the piece that THINK might fit one of your existing pieces?  I dunno, is that to many hoops to jump through for just a picture? It probably is.

Shops should also sell abilities.
If there's more than one shop in the game, the player can discover new shops by exploring. Maybe their stock should be random? If so, how to gate them away in ways that are not impossible to access?
If you have multiple shops, there should be 3 at minimum.

HP and hazards would easily provide some new things to buy or seek.
armor, max HP, heal, immunity against specific hazards
immunity against specific hazards = lock-and-key gating
It would be more interesting and fun to have that be part of an ability.

Zelda Link Between Worlds would be better if more of the abilities could be found, and if the rest were in multimple shops instead of just one. Then you could search and discover new shops with new exciting abilities to consider. And treasure chests would be must more exciting.

Zelda Link to the Past used big chests instead of random payout. This creates "scavenger hunt" gameplay. You know which chest is the "good" one, but you have to search the dungeon to find it. The big key adds another item to search for in the dungeon. That game is more about searching than finding. It works VERY well, but I wonder if adding "gambler payout" treasure chests on top of that would make it even better.