Well done in adding ways to earn points.
I'm not at all worried about skin being an "old" one, especially in a mid week contest. Infact it makes sence to allow folks who may have missed a skin or are newer to game to get it during a mid week. Of course weekend contests i would prefer new (or rare skins).
One suggestion, given participation is always lower during mid week contests, give skin out to top 10% not top 5%.
Btw top tier is a little underwhelming i imagine another 150 diamonds or 1k bazaar tolkens instead of ore would encourage the non skin hunters to stretch a little.