I have just finished transiting from a world that did not seem to have crystal caves into a world that I seeded prior to H&H and did not explore. If you just skirt the edges of a biome, that's enough to trigger generation and spoil the biome for new content. The unexplored pre-H&H world has crystal caves.

When you play on two worlds, you can use the resources of both. I have a ton of compulsively gathered raw material in world 1. No problem. You can overload your back-pack and haul a ton at a time because you are not going to do anything but log out and log-in, then drop everything. I literally went back for rocks.

And if you need thirty different things from a safe area, you can go back naked. All that moat digging is not lost.

I'm loving it. My new base is awesome and I have a new world to explore. My only beef is that the threat-level of events attaches to the world and not the player. I have not defeated Eikthyr on this world so I just get dinner-is-served events and I already have tons of boar and neck tail.