TBH i haven't had to deal with internal storage since I got a PSP Go.
That's probably the only reason I would suggest getting a PSP when the Vita is out. Go's are really cheap if you can find them nowadays, they have the savestate feature (that I don't think carried over to the Vita), and they're ultraportable and have internal storage. Their expansion storage used to be cheap too but recently it seems to have doubled in price. I remember the MS Micros being comparable to SD cards in price but now they're about twice as much. Still, unless you're packing music, movies, and games, I doubt you'll go through the 16GB with issues. My Go is full right now but I can easily remove stuff, put it back, or make room if needed.
That's probably the only reason I would suggest getting a PSP when the Vita is out. Go's are really cheap if you can find them nowadays, they have the savestate feature (that I don't think carried over to the Vita), and they're ultraportable and have internal storage. Their expansion storage used to be cheap too but recently it seems to have doubled in price. I remember the MS Micros being comparable to SD cards in price but now they're about twice as much. Still, unless you're packing music, movies, and games, I doubt you'll go through the 16GB with issues. My Go is full right now but I can easily remove stuff, put it back, or make room if needed.