The DS is simply not capable of good 3D graphics. I would much rather have nice 2D graphics than shitty 3D graphics. The game build itself was also sluggish and clunky. Coming after I had just played 1-2 GBA (which were extremely smooth and fast), the 3 remake was slow and awkward. The second screen was basically wasted. 4 has better gameplay than 3 for sure, but in terms of the presentation I don't see any reason to bother with the upgrade, for the same reason that I didn't think there was any point in buying the 1 and 2 ports on the PSP. Why bother?
FFIV is one of my favorites and I like seeing it presented in a new way.
And I never bought FF4-A.