Legendary Crate - Charm Set, Remove chorus flight and add in a set of Air charm, Speed charm and Void charm, all as 1 prize. They have durability and would help newer players massively as flight seems to be a key part of building and speed is also great getting around islands. I think this would be very beneficial to all players.
2. Remove the singular T3 Growth Crystal from Legendary and replace with 24 - 48 Red Fertiliser, which also speeds up growth and isn't extremely expensive, id much rather receive 32 Red fertiliser than a single T3 growth crystal, especially for Legendary.
3. Mystical Crate - Remove 8 Insanium, its extremely cheap to buy on market, with a shulker box containing 18,384 Essence (1728 compacted into block form) can be bought for a mere $10K. I think a Ultimate Induction Cell. Energy storage especially in larger format is fantastic ingame to keep a supply of energy going.
ps. If the crate key changes go ahead i can update the unofficial webpage. Hope these ideas can help.