I'm in a similar boat to you, currently running a mixed team with Unholy DK, Holy Pally, Shad Priest and Arcane Mage.

With ebon plaguebringer in effect on targets the dps jumps quite dramatically, and the addidtion of misery means less hit that I need to stack. I wouldn't think to swap the DK for the Pally tank because, like you, I just don't want the added stress of melee positioning.

At the same time, I'm absolutely hating the pally healing due to mana issues as well as the extreme lack of AOE heals.Before I got the pally to 80 I was healing with the priest, and 3 healing macroes covered every situation while never having to compromise healing ability to regen mana (S-fiend + 750/550 mp5).

I'm actually thinking of sparking my 4 shaman back up to join my pally or DK instead of continuing with this group as it sits, because it's just so much easier when any one of the dps can throw an aoe heal. For this reason I would suggest a shaman as your final position, for the totems + aoe/backup heals at need.