Excellent suggestions running the range of no work at all for the devs (edit a text description for clarity, and/or increase number of tiles affected) to a small bit of work (spell can't be cast within X tiles determined by mapsize variable of a city) to lots of work (a precast red/green indicator cursor highlight to show underlying fertile land available).
Crowdsourcing at its best!
I think for my personal modded version I'm going to go with description clarification and see if I can bump up the number of affected tiles. Should be a quick fix that will help balance the spell. Great ideas all around though.
Update: CoreSpells.xml description edited to "Revive the land. Works best near rivers, shards, prestigious locations and dragon statues.", radius changed from 1 to 3. Total time elapsed... 1 minute.