I think that coffee should give you more health, but I think that the speed boost is really good for something you can buy in an abundance late game. However, I think it should restore more health because it's often used in Skull Cavern and you often need help in there. Also, if you find yourself losing energy in Skull Cavern, here's my checklist for Skull Cavern Dives:
1. Buy Coffees and Salads from Gus (Coffee for Speed, Salad for Energy and Health) Both are cheap, making them affordable options for the late game.
2. Try to buy or make Desert Totems from the Desert Trader a few days before so you don't have to wait for Pam
3. Gather materials for or save up your Lucky Lunches and Spicy Eels (or make them if you can)
4. Leave all your non-usable tools (axe, fishing rod, etc) in a chest at home
5. Create a chest near the entrance of Skull Cavern to drop off your finds or tools (for drastic measures, don't leave Skull Cavern if you've gotten down pretty far!)
6. Dive!
I spend a lot of time preparing for the Dives, but it makes them so much more productive! Hope this was helpful for anybody out there :)