I think the current size is big enough. You can't see the ground from the top, even with visibility turned to max.
Ephi's elevators take more than a minute to reach the sphere (I got bored, so I don't have the exact time xD)
I don't think I'll ever build something taller than 500 meters. Cause that's just ridiculously large. This one was fun to build though.
The only thing I'm not very happy with is the interior:
What do you think? (It's not based on the actual interior, mind you)
To be honest, I don't have very much experience with interiors. Interiors aren't massive, they're delicate and small. I think that's why I don't like them very much.
If anyone wants to take a look at the save and spice up the interior, feel free to do that. I'd appreciate if you share the spiced up version with me after you're done.
Here's the save:
http://www.mediafire.com/?y176eglp16hbwxb. It includes the bricks needed.