I would if I liked the game. I buy physical carts on games even without the official case. The case seems to be worth more than the game in some cases because it's more collectible. However if I see any digital releases not being playable after X amount of time, I would reconsider.
Nope I wouldn't buy a case with a digital download code. Even the game key cards are slightly better than just a one time game code, at least when you get bored with the game key card game you can sell it.