Some things:
1) Corpse Party PSP is on Vita PSN.
2) You can also buy PS1 games on Vita.
3) New games come out every week on Vita including high-profile games. "Vita is dead" is just a circlejerk of people with shit taste or have to feel the hate boner of playing an exclusive game which they wouldn't enjoy if the game was on other platforms as well.
4) Zero Escape 3 is on 3DS, Vita AND Steam.
5) The 3D effect does not matter much. It does make quite a few games look pretty good, but the 3DS' graphics are still abysmal.
6) Vita homebrew was released the other day which means you can emulate the older Pokémon games on Vita.
7) 3DS seems to be getting fewer releases nowadays. 3DS is exclusive-driven, so there won't be much for you in 3DS' library if you dislike Nintendo. Shin Megami Tensei games (like 5 of them) are really good, and people love MH and Ace Attorney, so there's that.
Vita Slim's microUSB is enough reason to get it over the old model.
I have a Vita Slim and an OG 3DS, and prefer the Vita by far.
Edit: Persona 1 is seen as a pretty shitty game by everyone. Persona 4 Golden is a far different thing.