I've been tinkering with an idea for a space sym, kind of like MOO2, writing it for mobile or browser as a way to learn Java. Command ships and control planets, etc. I'd love to make the game in 3d, with x, y, and z coordinates to make things more realistic, but I'm afraid that it'd be too much to implement. The engine wouldn't be any harder to code, just add another vector to the calculations, but a user interface for navigating a 3d galaxy is more difficult. I'd prefer to keep the graphics simple, without a lot of hardcore rendering for different angles.
Does anyone have any experience designing a UI for directing units in 3D? If I decide to go the 3D route, how should I have the player control the 3rd coordinate (the one that would come out of the screen)? Is there a method that would allow a player to easily tell the ship how far "back" or "forward" to travel in addition to the usual up/down, right/left?