I'm not sure I see the point in paying any significant amount of money for eBook cover art, but to each his own. The average cover art for an eBook is going to be shown Icon Size on an eReader menu. No?
I agree editing is key and being able to pay editors frees an author to do other things. But wouldn't high editor fees equate to the equivalent of the "unpolished/lousy prototype" type project that this thread is saying shouldn't go through KS anyway?
My KS pet peeve is seeing typographic errors in project descriptions. What chance is there that the end product will be polished if the requester doesn't have sense to polish the request for money that they are putting out there?