Louie, look what I just found on Eurogamer - it's almost a carbon copy of my prediction:
"Sony plans to refresh the PlayStation Portable product line with a PSP-4000 model in late 2009 and launch a true successor - a PSP2, if you like - later.
Publishing sources, speaking to Eurogamer, were unable to provide any further detail on next year's update, which will presumably follow this year's PSP-3000 in taking an iterative approach. The PSP-3000 launched this October and followed a 2000-series model, the first Slim & Lite, in September 2007."
http://www.eurogamer.net/articles/psp-4000-in-2009-psp2-later
Even fewer details were available on the PSP successor, but we're told that developers are already working on games.