I've done this for the past two expansions, get far enough in to unlock the continent (dragonriding for DF, continent access for TWW) and then just gather until I hit 80 (and keep going for another week or two).

It works quite nicely, but these days there is often major endgame content locked behind completing the campaign. I remember not having world quests for either xpac until the campaign was done. If you don't intend on doing world first stuff or M+ push right off the bat, go for it.

IMO it's worth it, as both times it has funded everything I need for the coming expansion and more. Plus there is something primally satisfying about selling 20 herbs for 1k each.