I prefer the original GBA to the SP too
yes, the SP's screen is mighty nice - but I plugged in my copy of Street Fighter Alpha 3 into the SP - and I couldn't play it. For one, the buttons are too cramped (especcially the shoulder buttons), and they're a lot stiffer and 'clickier' than on the original GBA. They're also set into the unit more on the SP. Plus a proper headphone jack IS better. I usually play on the tram, to and from uni. headphones are a must (plus headphones sound way better than the puny speakers they stick in gameboys...)
So really, whilst a lit screen would be nice, I prefer a comfortable system, with controls I can actually use, over a light.
Besides, the original GBA looks much nicer too