With the xp reduction you can safely skip the collection quests in outland. The same cannot be said for northrend. In wrath it seems a collection component is mandatory for every major quest chain including the mandatory ones to open the rep dailies.

I suggest questing in Outland until at least 70, 71 preferably if you can stand the wait to get to northrend. There are plenty of non-collection quests to do in Outland that this is not even as irritating as it sounds and it will let you skip all but the essential collection quests in Northrend. If you do both start zones, all the zones in the middle and both end zones you should level fast without fear of running out of quests even if you have to skip large sections of quest chains because of the collection component.