I spent some time yesterday working on this problem. I had already put the aluminum tape in the bulb shrouds, but it was not good enough to make the cluster bright. Fortunately, the bulbs were clear--so I did not replace them.

At first look, the instrument faces look clean. But, I would never know how clean they were until I put bleach on them. I went ahead and disassembled the instrument cluster and proceeded with the cleaning. I scrubbed the numerals and let the bleach soak for a while. Then I blotted the bleach up with a paper towel. The case also had some dust in it, so I blew the dust out with compressed air. The lens of the case has been scratched over the years from cleaning. I went ahead and polished the scratches out. I also made sure the fiber optics were clean.

Last night when I went out, I would say the instruments were brightly bathed in incandescent light. They were about twice as bright was before. Even the black background was lighting up as well. I noticed the effect of the small alternator of these cars. I was running the heater at high speed, and when the engine idled, the instrument cluster dimmed. When the car started moving, the instrument cluster brightened. In the morning light, the numerals were nicely illuminated by the early sunlight--better than before. The instruments now look better in any light.

Incandescent bulbs tend to put out a yellowish light. I suppose the only improvement to the cluster now would be replace these bulbs with halogen ones. Halogen bulbs would put out a more white light, but I doubt halogen bulbs exist in this size. I worry about using LEDs. I trying to shine some key chain lights on the cluster but it looked bluish and spooky. I heard that someone was about to invent the white LED. The problem is that LEDs are too directional in their light dispersion to substitute for the original bulbs.

As Hattersguy, points out, these instrument clusters were designed for a high end car, so they left the factory looking bright. Over the years, dirt and aging bulbs have dimmed the cluster. An instrument cluster cleaning is definitely in store for those needing a brighter instruments.