I don't know why no one has ever brought this up until now.
There was a pretty big thread about it a few months ago.
My argument against it was similar to australian magics, but I also noted the disadvantage of not knowing if your opponent still has a unit.
example: get elefant, and if you manage to destroy all the enemy vehicles, get refund and spam p4s and ostwinds, your opponent pretty much has to play like you still have an elefant somewhere until there's enough reason for him to think you refunded it.
I will say though that I do like the idea, but I feel you should get an adequately small amount of resources back given the advantages it gives, getting 75%+ back for example would be awful.