buttons are cheaper, and only the top would need replaced....why worry so much about it?
I have my reasons

It's an important aesthetics issue and as much work I'm putting into this CP, I don't want to just use any random colored buttons.
If you've ever taken a button apart, the actual button part (that you press) is pretty simple. I've actually toyed with turning button tops on a lathe in hardwood. Then mating that top to the plastic bottom portion of the button (the part with the "legs" that latch into the button housing).
I have, actually. I have a set of six or so color mismatched buttons that I've dissected and examined.
On my cab, i've spray painted the buttons. I used a primer and good quality spray, then triple coated them in Future floor wax (yep), and have been VERY happy with the finish. It wouldn't hold up in an arcade, but it's done pretty good for my machine.
Never occurred to me to use floor wax. I do have white grease specifically formulated for plastics, but it's messy at best.
But real metal buttons (or turned wood) would be much better!
I concur, but I lack a lathe. Though I do want one and it is planned for, I just don't have the money or the space right now to dedicate to a lathe.
I think the biggest problem you might have in an all metal button is friction.
(unless they are ball bearing'd heh)
A plastic insert in a metal housing might be ok.
Nudge the button diameters an extra mm or two apart and use a vinyl collar somewhere down inside. I imagine that as long as you keep the tolerances loose, the vinyl would provide sufficient "lubricant" to the button. Unfortunately, that might be prone to gumming, but then regular buttons are probably prone to soda spills and rancid pizza grease as well.
In any case, I'm not entirely interested in an all metal button.