Heh, if only those were as plentiful as PSPs... (Amazon used pricing on Vitas is still practically retail price.)
But there are other reasons to get a PSP instead of a Vita. For one, if you have a large collection of UMDs, you'll want original hardware (although ripping UMDs is apparently easy now.) Then the Memory Card situation is a little better on PSP (you can just buy a sleeve for a SD Micro card and pop normal memory into it; Vita, you need to hack it plus get a custom sleeve to treat a SD card like a Game Cartridge, which takes a little doing.) And just pure ergonomics, some people prefer playing with PSP over Vita if you're playing PSP games or PS1 titles. Plus, some people have collector-edition PSPs, and just don't want these beauties to become trophy case items. If you can keep original hardware going, it's almost always better if you can to work for it than it is assuming everything will be BC or hacked to play later, even if there are benefits to upconversion/emulation as well.
(*If you're going to be hacking the hardware and ripping the software, there are other ways of playing your PSP or PS1 library too...)