Yes it's reasonable! Of course, I'm biased. I find that the hunter/priest combo works well for my quests, dailies and farming. I don't see why it wouldn't be just as good for leveling. The main thing that helps me (now that I've switched to making my hunter the main) are my priest's healing macros. I used to have my priest as my main (my first character and very nice gear) but things are 100% easier with the hunter as the main. I highly recommend going that route, but it seems you've already come to that conclusion.

My priest focuses my hunter. Then she heals her focus's target's target. So if my hunter is shooting a mob, the mob is attacking the cat, the priest heals the cat. When the monster suddenly attacks my hunter, the next heal goes to my hunter. I have just 2 such macros for the priest. One is a cast sequence with POM, Renew and PW Shield. The other macro is a cast sequence for heal, flash heal, greater heal. No macro needed for her Prayer of Healing, or group buffs. You might want to add a dispel magic/abolish disease macro as well. If after combat is over, I want to heal my hunter a bit more, I just target myself. So I'm my own target's target.

I'll post my settup when I get home from work tonight, just to give you an idea of how my dual-boxing works.