Yeah, if it means making a texture for the whole screen and then only modifying changed gauges.
If I do anything like that though, it would involve basically revamping the whole HUD system - not a fun task. How much performance increase would this give?
Edit: A quick idea for implementation - the hud rendering system is tied into the keypress system, so whenever a keypress event happens (let's say "fire afterburner") the HUD gauges are checked if the flag matches one of theirs. If it doesn't, the gauge isn't rendered.
Also tie it into the SEXP system, and main gauges flagged as being dependant on SEXP events would be updated when the SEXPs were updated.
Whenever a gauge is updated, all the mini-gauges are re-displayed onto the old HUD. The problem here comes in with text and different-sized images, and I'm not sure if there's a way to get around this...
You could make a gauge buffer for each one and then render that every frame unless the gauge is changed, i 'spose.