Actually I just got my second PSP, one of the new white ones with the Daxter pack (wanted to keep my 1.5FW for homebrew and programming).
And I noticed there are some improvements on that already. The battery definitely lasts longer. I'll look up some benchmark tests from the beginning of the PSP and run them on this new one. The d-pad also seems to have been lifted up a bit higher making it a lot more pleasant to use. The slight problems with the square button is also gone, but we knew that already. And the (Samsung) screen is indeed, as I already suspected from others, not quite as good as the Sharp one on my original PSP - there's a bit more ghosting on the new one visible when things are moving really fast. But other than that, the screen looks great and no dead pixels (again).
Really happy with Loco Roco (both demoes, the downloadable much better though - my girl already preordered it for my birthday, which happens to be the release date) and Daxter is great fun too. May get the 20 euro Burnout next (haven't seen Final Fantasy yet either).
Anyway, I don't expect too many other improvements. The DS really needed a makeover, but the PSP looked sharp from day one, if you ask me (I know, you didn't).
First we'll see the new peripherals. That GPS add-on should be really great, and who knows what the eyetoy for PSP will do. And of course the PS-One emulation, though I don't care too much about that - there are only a few games that I really liked on the PS1 (Micro Machines V3, which may still be better thoug than the native one coming up), the old Tomb Raider (but there's Legends now too), Tekken (but the real PSP Tekken is apparently great and likely to beat Tekken 2 and 3, though I would like to see the first person view back, that ruled in Tekken 2!), GT2 (but it's hard to go back, I'd rather not), Pandemonium (but nobody remembers that game), and who knows, FFVII (but I admit I just played from CGI to CGI really). Time Crisis also isn't going to be interesting on a PSP, but I would like to see the Pro Pinball series (Big Race U.S.A., don't know if the others were released for PS1, probably not).
Anyway, I digress. Point is, I doubt we'll see a different version. Just minor tweaks and improvements, as mentioned above, small increases in power efficiency. However, I'll be interested if Sandisk/Samsung manage that 32Gb memory stick.
I would like to see a tilt control add-on for PSP though.