A change is as good as a rest, as the saying goes.
I think switching to another character has reinvigorated my Warcraft playing. I've been switching back and forth between my main and alt and have got some of my mojo back. The catch-up mechanisms in place will have something to do with it — being able to level things up a lot quicker than you normally would — but it's not just that. Being able to just play solo, without any pressure, is just what I needed.