I agree with phyrne :V
To answer your question, you should probably get to the places/quests you’re unlikely to visit with your alts; you can get one Ambition per character, for example, so unless you were planning to play the same Ambition in the same way with another alt, getting to the end of that would be a pretty important point. Apart from those, however, I don’t recall places or massive amounts of content that are mutually exclusive with each other?