For the FPS drops: Yeah, the camera just does that. I'm guessing it has to do with how the lens filters the light so I don't think it's fixable, but I'm no camera expert.
IIRC I read somewhere that the board lens have an aperture of 13, so obviously the lens has very poor performance in low light conditions, but it dosen't change the clock cycle of the CMOS image sensor. I think it has to do with how fast the CMOS image sensor process the black pixels, but I don't know. That's why I wondered if overclocking the GBA would do any difference. Or does the camera have it's own oscillator? According to the M64282FP datasheet it has a system clock of 500KHz, so if it pulls it's clock from the GBA there is a divider inbetween. So you could either change the divider or overclock the GBA. Providing the camera won't crash. Does anyone have schematics for the MGB-006? I'm also very much interested in the japanese version aswell.
You can also change the board lens that is mounted on the CMOS image sensor. It's basicly something like this, but not the exact part, it's just an example: http://www.ebay.co.uk/itm/Safety-CCTV-C 43bdc2a453
And you can get different lenses that will screw onto the holder like so: http://www.ebay.co.uk/itm/Safety-CCTV-C 43bdc2a453
Different lenses has different focal lengt, aperture and angle of view. So oviously if you use one with a low aperture, image quality will increase. I'm wondering what results you would get with a better board lens, and overclocking. Hmm......