It's not like we have Valkyries, Bastets, Isis, Haku, Krakens, Anubis, and Amons altogether to skill up. :/
I would burn stones for stamina but my TAMADRApurin friends aren't even on yet.
That said, I've had incredible luck with Valkyrie skills. I've run the dungeon four times for the free stone and I have three skill ups already.