No, you're not the only one who darkens the dash at night. My Saab 9-5 actually has a "night panel" button that shuts off everything but the speedo; if anything goes "critical" (low fuel, etc.) the relevant display lights until the condition is corrected, and if one changes the radio or AC settings those displays light temporarily. It really does help a bit on rural, light-traffic freeways. Besides, it feels kind of cool..
