I think the trick is to make it really easy for folks to avrtel quickly if they feel like it, with the occasional inter-zone quest (with under 10 minute avrtel) so that you're not just churning through the content in one spot, never to see it again when you exhaust/outlevel it. You then add points of interest with optional goals/quests to entertain people who're in the mood to just pick a direction and see what's behind that ridge on the horizon. Obvious Time Sinks are like pebbles in the shoes, and these sorts of quest paths are definite OTSs.