- Gradients: Tetsujin, sorry you don't like the gradients. I thought the inset metal panels idea was pretty neat. I'm just looking for a control panel art concept that hasn't been done a lot, so I'm trying to avoid the typical vector outlines. Though, as you say, the gradients might turn out tacky. I'll have to see what it looks like when I test print it at full size.
I'm sorry I couldn't offer anything more constructive there. I don't have the expertise of a designer, to say, "Oh, this would be better because of this reason and that reason, etc.". So you could take my comments as reflecting my personal tastes. But maybe I can provide some more useful information.
The metal plating idea is interesting, but I'm concerned that in practice it'll just look like "noise". When building a model of a sci-fi ship or something like that, the "noise" in a pattern like that lends the otherwise monotonous forms some depth. And if you get really advanced (with things like the pearlescent and gloss-variation layers of the Star Trek ship painting patterns) the effects can be subtle and impressive.
In the case of the CP, however, you've already got the design punctuated with the colors of the controls. The red sticks and trackball will stand right out. I feel that some aspects of the CP artwork should balance that. The plating pattern could be fine if maybe it were punctuated with some red trim or something. I'm not really sure.
The gradients around the control groups, though... I think as simple gradients they'll be a bad idea. This is largely a gut reaction on my part, but maybe I can justify that a little. First off, it's gray on gray, with no variation of hue or anything like that. The only way it stands out from the background is by contrast: and since the gray value changes across the gradient, that distinction from the background is not consistent. I like your basic patterns, the simple shapes around the control groups punctuated with gap lines (especially the upper controls - I think the joystick spaces could benefit from having similar gap lines of some sort). But I think that the distinction of those areas relative to the background should be more secure.
I think making those bits have a brushed aluminum surface (simulated or otherwise) could be just the thing. The control-group areas will be set apart because they will reflect light differently than the printed gray background. You could do that with self-adhesive foil, I imagine, if you cut it carefully enough. You could also use metallic paint sprayed on. If you used actual metal plate for those areas, that would look even better.
However, I think in any case the design would benefit from some color. Consider how sci-fi ships are painted: The movie-version Enterprise had some blue regions on the lower hull. The Millenium Falcon (and other Star Wars stuff) had regions of deep brown-red. Babylon 5 stuff is punctuated with blues and greens. But most important is the fact that your controls have color, and I feel like that overwhelms the grays. The design of the panel art should fit with (and complement) that.
That's just my two credits.