Once dual specs are in, this won't be much of an issue.
Until then, consider two moonkins and a dreamstate druid.

For me, dreamstate was able to heal effectively at the BC level for all heroics and raid content. WotLK heroics seem to be much easier at 80th then BC heroics were at 70th; I don't think you'll have issues healing them as Dreamstate.
For an 80th druid, go down to Moonkin form in Balance and to Swiftmend in Restoration. Be sure to include Moonglow, Lunar Guidance and Dreamstate in your Balance tree.

Regrowth is your primary heal, and with the glyph its a lot better then Healing Touch.
Keep Rejuvenation up all the time, and Swiftmend it to counteract burst damage. Lifebloom up all the time, its not as good as it was, but still very worthwhile.
As a dreamstate, you can dps better then any other healer spec, and are a capable healer too.
The only real weakness compared to a deeper resto druid is the lack of the AoE heal, aside from Tranquility (which should be every 4 mins as Dreamstate). If AoE becomes an issue, you can hotkey Tranquility in some kind of a rotation for the other druids too.

I made a macro for my druids, something to the effect:
/cast [nostance:6] Moonkin Form.
Not sure the exact stance, but its easy to figure out which number to use, from left to right your stances start at 1 with each form you have.
The macro will let a druid not in their moonkin form assume the form, without taking a druid already in moonkin form out of it.
So, when things are weaker, put them all in moonkin for the extra damage, but heal whenever you need to.