I think there will be a PSP-4000 before there is a PSP2.
And yes, I think PSP sales will pick up this year in America -- DS/DSLite owners are eyeing it as an upgrade, instead of the DSi I think.
Remember that when the PSP-2000 was released, Sony effectively increased the speed of the PSP processor to 333 MHz, by removing the firmware cap on it (it had been capped to 222 MHz for the first couple years, and 277 MHz only after the release of Ratchet & Clank: Size Matters, as I recall -- battery reasons). The 333 MHz "upgrade" effectively coincided with the release of God of War on the PSP -- and I think the reason is obvious.
This "bonus" speed increase would have had an influence on game performance in the past year, but will start to have an effect, from a PSP game design perspective, starting this year (since games releasing now were very early in development when they got news of this speed increase, and could be adjusted to benefit from it). The PSP games coming out this year are thus, a little more ambitious, and it'll probably show in terms of quality.
The current PSP models are damn near as fast as a PS2 -- faster in some ways -- and they have 64 MB of memory to boot. I would not at all be surprised to see a PSP2, in ~3 years, that sported a 848x480 LCD (the PSP1 is 480x272), and perhaps even had the ability to play downloadable PS2 titles from the PSN, as well as PS1 and PSP1 games. It could have the horsepower of a Wii, easily.
