My thinking on the mistlands update is that H&H changed so much about the game mechanics I doubt there will be another update that changes so much. I could be wrong; but that's what I'm going with for now. So with that in mind I think that now is the perfect time to restart. As long as you don't explore past the halfway point towards the edge of the world you can play all the current content now and still do all the future content from that same world.

Q: Having beaten the game to death before H&H, is it worth coming back now?
A: Yes, I think so. So much about the game has changed and there are new structures to build at every stage of tech progression.