Don't forget saving them up to use for "Abusive" wishes. ( I wish for ... abuse! )
Armor of Virtue takes astral, I think; those lances everyone always wants for going against Ermor; some ... old banged up beer stein with a "Monty Python was Here" scratched on it.
And don't forget to save enough for Christmas, when every new born unit wants a nice Dispel to get get of the Curse of Time and other unpleasant global enchantments that make someone else think they're God or something.
Honestly, I never thought I'd see someone asking for things to do with Astral Gems. After all - there's always alchemizing into earth to sell for gold, or turning into water gems to make clams to generate .... more astral gems!
(Seriously though - don't alchemize into earth. It's better to alchemize into nature or some such, because Nature lets you sell Wine Skins to the local drunks.)