What about a joystick button? You could push the button to download frames from the robot or something similar. This way, you don't have to always be situated with one or the other -- HUD/No HUD.
I'm sure that a HUD would be most useful with some sort of tracking system, where post-processed data could be displayed. Distances to known objects could be printed on the object. Alignment could also be displayed.
For example:
Code:
TARGET POSITION:
10 degrees right
12 feet forward
SHOOTING POSITION:
10 degrees right
Move forward 2 feet