You know I just did this with my 70 hunter and 4 lowbie shaman. Works great for the 4. Yes it is effective. Yes it will most likely go faster and definitely more predictable and brainless than leveling 5 characters through questing (in most scenarios.) but here's the issue you'll run into:

You will loathe coming back to your pally.

You will think "why should i bother with my pally, when I still need to gear up my other guys?" If you really bite the bullet and come back to him, you'll hate life slowly leveling on quests, and you'll have this thought in the back of your mind, "If i'm going to relevel starting at 23 again, why not just level up 4 more characters to go along with this guy? it's just about as easy" so then you'll be back to square 1.

So effectively you can say goodbye to the idea of having a pally for a long time if you choose to do this. That might be worth it to you though, to get your 70 druids faster. If you want a 4 druid + pally team, don't bother doing it. If you want a 4 druid + lock team, go for it.

hope this helps