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"Asleep at the switch? I wasn't asleep, I was drunk!" - Homer Simpson
 

You have a valid concern, I suppose, but all our back-lit cases are wood, with flourescant fixtures and diffusers installed on the inside and a metal one-sheet frame around the outside. They look and work great. Besides, if bad wiring or ballasts regularly caused fire problems, you wouldn't see any buildings anywhere with lights in ceiling tiles, or any dry wall or carpet or wood anywhere for that matter. I think the development, testing, certification, and insurance go into the fixtures and ballasts when they are made, not what you put them in.

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"Asleep at the switch? I wasn't asleep, I was drunk!" - Homer Simpson
 

As for ceiling lights and wallboard, drop ceiling fixtures are specced NOT to have insulation around them or be surrounded by flammable material unless they have an approved design. Wallboard is not combustable, and in fact is a fire retardant. The gypsum compound in wallboard breaks down with relatively low heat, and the major byproduct is steam. That means that until all of the wallboard has changed state, nothing on the other side of a sheet of wallboard can get above 212 degrees F. Fire safes are made from layers of gypsum board or plaster of paris for just this reason.

Cost of development has to be amortized over a product run. By the time amortization wears out, usually inflation works to keep the price of the product just as high unless there are other cost savings factors at work.

I understand your point that things seem to be working out well for you, but by the same token I could just as easily describe how to make a wooden lamphouse for xenon short arcs. It would work, and probably never have a problem, but wood is just not as well adapted for the job as metal.

For the few extra bucks to get a professionally made display, the added safety is worth the expense. Also, there are a number of dead theatres now, and picking up used cases on the cheap should be possible.

You might be able to laminate wood paneling over a metal case to create a more organic kind of look. However, the general design convention is to have a low profile case in either black or some architectural dark bronze color.

Metal and types of plastic are much better for use in various point-of-purchase displays, such as a poster case. With something like an aluminum extrusion kit, you can incorporate all the electronics, lighting, ballast, etc. into a self contained unit. The case will be heavier and a bit thicker, but the upshot is you'll only need to make one wall penetration for electrical conduit to conceal the power source. Using a thinner case made of plastic might require things like the transformer to be remote mounted up in the drop ceiling (this is a pretty common item with neon signs mounted on clear acrylic).