First of all you have to take into account that the SP didn't arrive until 2 yrs after the original GBA was released.
As for the DS's physical design, I have realized my beliefs:
1) Should Nintendo 'tweak' the DS's design? A: Yes, certainly.
2) Do you trust Nintendo to do it? A: No, not really.
Again for the possibility of an SP edition, we need to think of two factors: Need and Cost. What more does the DS need to be substancially better, but still retaining the original gaming function? I can't think of anything, maybe the controls could be an issue, but I'll wait until I have actually tried the thing. And for cost, can Nintendo afford to release two editions of such a risky system, when using the redesign from the beginning will improve the DS's overall chances of success? Frankly, I don't think so. To be honest, I'm very concerned about the cost of the system anyway, and I could never imagine myself paying $240 CDN for a portable, and $50 for portable quality games. Sure, you could argue that it's warranted by it's never-before-seen gaming, but that just isn't enough for me. And I think this could pose a serious threat to handheld gaming, in my opinion, because the only other option I have no hopes for (simply too expensive). But now it seems I am changing subjects.