I too have a GBA... and this new version, the GBA SP, is basically an admittance by Nintendo that they naffed the first one up.
It's the same hardware in a new flip-top case...
but
They've added a backlight to the screen, and it has an in-built rechargeable battery which is good for 10 hours with backlight, and 18 without.
One of my biggest complaints with GBA has been that you really do need perfect lighting conditions to even play the damn thing - Castlevania: Circle of the Moon was nearly damn unplayable due to the overly dark palette Konami chose.
I wonder what Nintendo are going to do for those of us who bought GBA on day of release (like I did)... This is as much a smack in the face as Konami releasing MGS2: Substance is... I don't think it is right I should be expected to buy a product twice in order to get the 'fixed' version...
Grrrr....
- S