Hiding in plain sight was Bukkit's built-in support for multiple worlds to exist on the same server, relying on various plugins to handle players moving between them. With that found, and a couple new plugins installed, there's now a second world on the server to explore and exploit.
How do I get to this fantastic new place?
You enter the stargate, of course! Within the spawn point sphere of protection now exists a stargate. Right-click on the sign to select your destination (right now only World 1 and World 2 available) then click the button on the opposite side, and KAWOOSH! Wormhole formed, enter at your own peril.
Both worlds play by the same rules for now and, as always, try to move away from spawn before building. For instance, I'm 1km (1 block=1 meter, so 1000 blocks) directly west of spawn. The respawn point is at 0x0, so it's easy to find and easy to know how far away from it you are. Try to move at least 250 meters from it before doing anything. If you want to build a bridge, road, tunnel, etc. closer to it, post your intentions here first and get some feedback and consent.
In the interest of this new world being a "fresh start" each world has its own inventory. That means no carrying resources from one world to the other. Get ready to build that awesome wood pick again!
As for adding yet more worlds... I'll need to research how resource requirements change with multiple worlds first.
EDIT: Sigh. Hold that thought. The button that activates the stargate can't be triggered by non-admins in the spawn zone. Grrr.... I'll have to move things around... and find some other way to protect the gate.
EDIT 2: Okay. Sort of got it fixed. I disabled the normal protection and defined the area as a "region" with WorldGuard restrictions, which gives more precise control. The stargates should work, while building/destroying is still prevented.