I thought I'd do a mod that my wife can actually understand and would like. I found this piece at my local Schucks auto parts store, it's a lighted vanity mirror that takes 4 AAA bateries.
It's also avaliable from www.schucks.com (part 449x)
1. Remove the sun visor from your car
2. Remove the factory mirror from the sun visor - There are only plastic prongs attaching the mirror to the visor which come off pretty easily if you just pull it.
3. Place the vanity mirror onto the sun visor and measure and mark the placement.
4. break out the exacto knife and gently cut the top layer of plastic around 3/4 of the length of the entire vanity mirror. Cut each end into a T shape.
NOTE: do not remove any of the top layer of plastic.
5. There are 2 layers of foam and then finally a layer of cardboard in the sun visor. Cut away all the foam around the outline of where the vanity mirror will sit.
6. Use double sided tape to attach the outer layer of gray plastic to the cardboard.
7. Attach the vanity mirror to the Sun Visor using double sided automotive tape.
8. Put in the batteries and put the sun visor back in your car.
9. Remove the lack of a lighted mirror from your girlfriends WRX pet peves list.
Soon to come, recovering the sun visors! If you do this right recovering them won't be nessisary, but I don't like the cheap plastic