Here are my thoughts. If you (the global you) copy a card and just change it enough so that nobody notices and then you sell it or enter a contest with it, that is wrong. Your intent was to steal the design and profit from it in some manner.
If you see a card and change a few things to make it your own, you have been inspired by it.
It all goes to intent IMO. Since that is difficult to prove, only the creator knows if it is morally or ethically right or wrong.