Crap, grinding won't work here then. I guess I'll have to adjust to the questing as well. I plan on starting my new class now (probably Druid or Shaman). Any suggestions/tips for a DPS based one? Also, would I still be able to be the healer of the group if I have the healing skills but didn't choose the healing talent tree? I noticed waiting for groups to dungeon sometimes takes quite a while at low levels and I figure if I could help out with healing just to get the dungeon going I wouldn't mind.
Shorter version, I'd like to be able to choose healer during that role window that pops up when you first decide to join to get it started, and if we have another healer that could handle it then I could just be another DPS, or if we really need two healers I'd just suck it up for the time it takes to finish the dungeon.
At very low levels you might be able to get away with healing a dungeon even if you're not specced for it, but it isn't recommended.
Let's take a shaman. Suppose you were an Elemental shaman. You could probably get away with healing some of the low-level instances, since Elemental shaman uses the same gear as Restoration. Now let's suppose you were leveling as Enhancement but wanted to try healing. You would probably do terrible because your gear doesn't match up with the role. Enhancement shamans use Agility and do not stack for Intellect. You will probably run out of mana very quickly.
Either way, I wouldn't recommend you heal a dungeon if you're not in the right spec for it. For one, you won't have some of the core talents and abilities you need as a healer. Back to the shaman example--when you choose the Restoration spec at level 10, you automatically get the Earth Shield ability, as well as the passive abilities Purification and Meditation.
Purification: "Increases the effectiveness of your healing spells by 25%, and reduces the casting time of your Healing Wave and Greater Healing Wave spells by 0.5 sec."
Meditation: "Allows 50% of your mana regeneration from Spirit to continue while in combat."
You may think that both of those passive abilities don't sound like much, but they will make a huge difference in your effectiveness as a healer. Put simply, if you're NOT a Resto shaman, your heals will be 25% weaker, 0.5 seconds slower, and Spirit won't help you regenerate mana in combat. Maybe in an instance like Ragefire Chasm you might not notice much of a problem. But get into something more challenging like Shadowfang Keep and suddenly you might have a problem, especially if you get a poor tank or some clueless DPS.
Another reason... many other players you might run into in dungeons can be fairly unforgiving. If you queue as a healer in a non-healing spec and something goes wrong (even if it's not your fault), the first thing people will do is check gear/talents to see if there's a problem. If you're not what they're looking for, they may yell and blame you for the disaster, or even kick you from the group. :\
Also, if you picked "healer" role to queue as, hoping that another healer could come in and take over, you might just get tossed into a group where you're the ONLY class able to heal. (Warrior, hunter, rogue, mage, and then you, for instance. xD) Then you'll have no one to fall back on if you find you're not up to the challenge.
There are exceptions, and it usually depends on how experienced you are with the game and the roles your class can play if you can successfully get away with playing a different role. But in general you're kind of limiting your performance if you're not in the right spec. (And you definitely can't do it at end-game.)