Siphon aside the only thing I can think of that SE did to spirits was adjust their behavior in casting spells, and the spirits spell repetuar. The only real problem that spirits have is an unreliable nature when it comes to casting, but I think you should take it upon yourself to find a practical use for these spirits to at least give them more meaning.

Example: Use spirits to help with yellow triggers in abyssea. They won't have all the spells but still have a few of them to use.

Additionally I would like to move to give Sprits updated spells to augment them with the recent level increase.