It can be improved with meta staples like Robin Hood Champion of Sherwood or Beast Tragic Hero
Each play booster can contain up to four total rares, so the theoretical highest number of rares you could open is 120 (or 144 for 2024 play booster boxes), though you should be playing both the lottery and lots of Sealed if youre that lucky
Amber and Ruby would also pair nicely, for challenge and healing abilities
And the deck isn't even technically an Elf deck, but with 12 one drop mana making Elves, plus 4 Priests, and 4 Circles, you have 20 Elves that tap for mana, then flesh out your deck otherwise
If you're interested in getting started selling alters, here's some advice
The Wayward Sorcerer might not be the most playable card on this list, requiring you to build around Broom cards, but it still demands a high value given its Enchanted status and beautiful alternate artwork