Other than the reputation gains from instancing first and questing later, I don't see it as a major issue. I personally stopped cashing in my quests for my hunter (my farming character) partway through Nagrand, also leaving BEM, Nether and SMV for straight cash. If I had finished off the quests though, there is still a lot of cash to be made from just plain killing things anyhow. I cherrypick the ones that are worth doing as it stands anyhow, it's just that so many are made easier by having a flying mount.

Of course efficiency is not the only concern though and people should do what they find most fun.

I did all solo quests in Hellfire, Zangar, Terrokar and Nagrand. Only ran a few of the group ones (I mainly soloed to 68). I grined Ogres all thru 68 and got exalted with Mag'har along the way. Will now continue grinding other mobs that raise rep for Scryer and Consortium for 69.

When I hit 70 I will have Blades Edge, Netherstorm and Shadow left to get gold from. I already have 2k gold from grinding and selling drops (to vendors not the AH).

Yes I didn't rush to 70, so rested xp takes a part in this.