Personally, I think it is only deserving for 1st and 2nd to receive the mark/nymphs. If anything, to raise the prizes, a shard code for 3rd and 4th, 5th, 6th receiving the usual electrum reward.
But let us not forget that until recently we only had 1st, 2nd, and 3rd prize, with 1st being 5k and the only one with a nymph, so I guess it's quite better than what we had last. I'm satisfied with it.