Tim -
After you learn the site, it is a wealth of info and is pretty easy to navigate. For instance, it's very easy to enter a 6v bulb number and find the exact 12v equivalent.
Regarding brighter bulbs for your instrument panel - I searched for 12v bulbs with the same size base and glass, and that have more than 0.16 candlepower. (#57 12v instrument panel bulbs produce 0.16cp)
< CLICK for search results > Click on each bulb for more info.
My concern with using brigter bulbs is that they also produce more heat that could damage the graphics on your gauges.
Also, your bulbs may just be getting dim with age (bulb age, not your age!) A new bulb - same bulb # - will probably be brighter than one that has been in use for a while.
Here are instructions for searching the bulb site:
< CLICK instructions >