How viable would a PSVita be?
To me, it would seem that the biggest issue is removing the screen (which is firmly glued under a large, plastic cover). The rest of the PSVita is incredibly modular. After that you have the 2 Input Controller PCBs. They're ultra modular, but they connect using some rather tiny ribbon cables. The joystick units themselves are definitely really nice, but they too use small ribbon cables.
Would a PSVita be worth the effort, if only to avoid the terrible Thumbstick on the PSP 1000/2000 models?
Thickness of the Vita would make this difficult. With a custom board you could probably fit at least a Pi Zero and get all the controls working. It's hard to tell whether there is enough thickness to fit an LCD controller.
Love your site. Seems like the PSP is the best form factor I've seen on the interwebs. I also noticed a bunch of broken PS Vitas out there. Any attempts at squishing in all the components since this post 12 mths ago?
Unrelated - do you ever sell complete PSP 1001 units (without SD w ROMS to keep the lawyers away)? You must have a bunch of cases lying around.