Well, for starters I have to this day never paid for a GBA. I've found an SP in the woods at the park, and later had someone give me an original GBA because they didn't want it. I actually paid for a Gameboy Player to play Metroid Fusion, Zero Mission, and the Castlevania titles with it. Most of the games being released were awful rehashes or tv/movie franchise cash-ins, so there were no must-haves on the GBA to kick things off. The no-light thing? Yeah, I wouldn't own an original GBA if I had to pay for it.
The sound hardware is an amusing point, because the GBA does have the same sound hardware as the GBC - for GBC games. It also has GBA sound hardware for GBA games. The GBC had no midi-tables, with much-more-simplistic synthesizers and very, very, low-memory support for sampling.
The screen resolution quip means that there was no increase in pixels displayed in the same screen space, it was literally the exact same resolution and AFAIK the exact same size. I mean that the dots on the screen should have been smaller, and there should have been more of them in the same alotted space. A standard 4:3 ratio screen would've been a plus, too, but they stuck with their 1:1 ratio. As a result, the lower resolutions hurt gameplay: SMB, for example, became much more difficult to play on the GBC as it lacked available space on screen to display approaching obstacles and enemies. If you'll notice, the objects in the original Super Mario Land are
very small, while the objects in SML2: the 6 Golden Coins are larger, but the speed of the gameplay has been significantly reduced to accommodate the small viewing area:
If I compare the NES to the SNES, there was only a 5 year gap in releases for that CA-RAZY jump. The GB to GBC was a 9 year gap. That's 4 more years for a lot of nothing new.
Sega's tank with the DC was due to timing, bad reputation, and a pathetic budget for advertising. By ingloriously dropping support for the Saturn, 32x, and CD systems, Sega insured that many onetime fans were no longer supporters. The timing was bad for Sega because they'd only dropped Saturn support a few measly years prior, and their hardware could've been cooked a bit longer, frankly. The advertising budget was what hurt them most, though - the company literally didn't have the cash to float the system on the market. Also, considering their history with the Saturn, they'd burned a LOT of bridges with the stores they'd need shelf space in.