Well, backlit or not, the DS Phat has really bad screens, especially compared to the DS Lite. Not only is the brightness ridiculously low, but the color has nowhere near the fidelity or quality of the DS Lite. In more ways than one, the DS Phat has more things in common with the SP than the Lite. Too bad the Phat and Lite screens don't appear to be compatible, otherwise I'd open up another DS Phat and stick some replacement DS Lite screens in it.
1) The DS Phat is frontlit only, though I'd LOVE to hear news of a backlit version, since I can't stand the DS Lite.
2) The GBA SP2 is available in only 3 colors: Graphite, Pearl Pink and Pearl Blue. I've heard there were also two limited edition AGS-101 variants, Special Pikachu Edition and a Spongebob Squarepants version.
3) If your hardware is wearing out, don't throw it away, fix it! Search around, you can probably find NOS contact pads for the Micro somewhere.
Hmm, yes there's a very real possibility you damaged your Game Gear. When there is a fault in the system, the GG likes to turn itself off a moment after you flip the power on. Probably a safety measure.
There might be a voltage regulator at the very least inside the Game Gear. If there is, the bad AC adapter would probably break it before damaging anything else inside the GG. I don't off hand know if the GG has a voltage regulator, or any other kind of power safe guard, I'd have to look it up or look through my physical GG systems.