For your question, I managed to only quest through 2 zones in outland leveling my latest alt. I did helfire and part of zangermarsh. Its all worth seeing, if you never have, but I also used the dungeon finder because I like the outland instances.

As for the dual specced folks that zone in as said 'other spec' and not being prepared, I see the opposite opposite of that. In that I see tanks that zone in, I've seen tanks that come in and have issues with trash pulls or say the trash pulls go fine but the boss fight is tricky. The finger pointing starts the first time someone dies. Tank points at the healer (wtf dude!), healer points to the dps (where's your 40k! l2p!) and the dps give the o.O face (uhm we're TRYING but tank forgot to keep threat and I got eaten). A few pulls and lots of bitching later, tank says, hey i'm tryin but I usually dps. Then *I* have the >.< face like geez dude WHY queue as somethin you don't do. This happened throughout leveling, not just in Cata dungeons, but I have seen it a lot more in the catas.

Makes me glad I haven't been actively healing. I'm a shadow priest, dual specced disc. I'm mostly dps, I heal for guild runs because one of my guildies leveled a tank and the insta-queues having both a tank and a healer were just too good to pass up. I've enjoyed leveling healers in the past, I hadn't intended for this priest to heal, but I don't mind. I like playing a utility class because I can be helpful if the healer goes down.

Good luck with whatever you choose :)