After playing my little trial L15 Spellsinger I had a thought: can a high level Spellsinger zone in with your much lower level char, tap it with inspire, then leave? Well, I'm pretty sure it can, but without zeroing the XP? I can make arguments for both sides of "should" on that one. So, I'd have to test it or hear from those that know already.

Doubt I'd ever bother going to that effort, but the duration and non-dispellable nature of a fully enhanced inspire could easily carry a lowbie through a very long quest. Those are very nice buffs!