If you have no other gear than your resto gear, I would suggest to respec elemental to do quests. That's what I did anyways. It was fun, but I felt like I wasn't doing good enough damage, even though I was using my S3/S4 gear which had lots of crit which is good for elemental.
What I did was gather as much Northrend quest rewards as I could for enhance, and once I was able to get a decent set, I respecced. I found that I can kill stuff way faster as Enhancement than Elemental even though I had greens!
If you really love to heal, I would suggest leveling to 78 or so and then healing from there. It would enable you to grab decent gear till 80. I'm level 79 right now and I'm just going to grind to 80 and then respec Resto!
Have fun bro, that's what is most important ;).