I'm running a team close to yours, and I know I'd be sunk without my holy priest. My Boomer is my backup healer, and can throw the occasional heal when I need it, but my Boomer's job is primarily DPS, and she's very, very, very good at it.

If it were me, I'd drop the hunter, and either level another druid and go Resto (UBER group HOT healer), or raise a Holy priest. I'm just starting Heroics, and while you'll have DPS, you'll be getting smacked around pretty hard until you badge them up.

The mixed nature does not have to gimp your dps, as stated above - I have my 3 dps hitting 14-15k reliably in Heroics and 17-19k easily in normal dungeons. That's plenty of dps, and it will go up once I start badging - and I'm going to play with a suggestion made here and throw some shadow spells on the priest's macro for the extra DPS.

My #1 concern in Heroics, even with my pally at 540 def cap, is keeping her alive, and I would lose all of my Boomer's DPS healing her, and I don't think it would be as effective as making her Resto, and switching in a new DPS to replace the priest.

Put it this way, if you put your group together with other players in the game, it would wipe. The typical group is tank>healer>dps>dps>dps. The Boomer can heal, yes, but it's no way as efficient as a dedicated healer.

But that's my opinion. When you get to Heroics, I'd love to see you prove me wrong, that's how we learn.