well, its the brightness, really. Developers brightened the color palette for the SNES ports so they could be seen on a standard GBA that has a darker palette. Good for the handheld, bad for the TV. Plus, the SMA series made a lot of Mario fans angry. We just wanted Super Mario All Stars ported and we'd be happy. But Nintendo went and re-released all the titles sepratley. So if you were to get Super Mario Bros. DX(SMB1, SMB2J), Super Mario Advance (SMB2), Super Mario Advance 4 (SMB3) (and Super Mario Advance 2 for SMW if you got that bundle cartridge) Thats like $90 ($120 with SMW) VS. $10-15 used All Stars cartridge. Play it on the go? Thats a good point, but if you could play it at a slashed price, its better to just go for the cheaper alternative (And the alternative is actually good)
But if your an insane fanatic like me, you'd get All Stars and the Advance titles. But meh...
But the GBA does well with new titles. The new Mario games (Wario Land 4, Mario & Luigi, Mario Kart Super Circut etc. etc.) Are awesome. Dont even pass them up.