You might consider changing them to LEDs if you are going to make them brighter.. The LEDs will wont get as hot as the incandescent bulbs..
I replaced all my 921s with LEDS. I used warm white, this is about the same color as the incandescent bulb.. I bought them on e-bay. I think I paid about $1 each..
LED Conversion – 1999 Southwind 35S
These are polarity sensitive, so it they don't work, unplug them, and flip them around in the socket..