First of all, welcome to NICO.
The odd flap in front of your visor is a mini sun visor for those times when the sun is positioned directly between your two sun visors.
The button that appears to be useless is for a mini dome light. It's a very faint light that only comes on if your headlights are on. Try it at night. It should illuminate the area around the gear shifter and part of the radio. You have to try it when it's REALLY dark to be able to tell.
Check out my J30 web page for some good J30 reading...
http://www.fuzzycats.com/j30.htm
Carlos