I understand the frustration of quest completion in that range. I have a priest and a hunter that I've been leveling almost side by side. I found the hunter is able to complete quests at or above level far easier than the priest. Certain quests were downright impossible for the priest to do alone (the giant on the shore in Stranglethorn, for example.)
I found that I had to be selective on quests for the priest. If I came across a quest that I could not complete, I skipped it and went to the next. I did not abandon quest (something of the completionist in my blood =0 ), but I did not bang my head against the wall trying to do it right then (that giant died a miserable death about 5 levels later!) If the zone you are in does not have any easier quests, change zones for a few levels and come back. I suggest doing quests 2-3 levels lower than the toon for the priest, just to stay ahead of the curve.
As far as gear goes, I was taking everything that built up intellect, but neglected to boost spirit as well. It was around level 30 that I realized that having a lot of mana is good, but regenerating mana fast was just as important.
BTW, I had a hybrid build through those levels, but I remember that after getting Spirit Tap (I know it is Shadow!), the grinding time and mana breaks dropped substantially. If you're toon is dead set against Shadow, no worries, but a little Shadow never hurt anyone. =)