Ah - I'd expect that the visuals on the PSP version are probably better due to the hardware, but it's not as though I'd expect anything's been redrawn.
I didn't have my own PSP copy, probably 2-3 years back. I was 'borrowing' it, so just loaded it up to take a quick look before 'returning' it. Looked interesting, but I'll eventually buy and play the original DS version in earnest, with the d-pad + touch.
It's in the queue, but I know that once I buy a DS, it'll eat time that I really need to use for other things right now