The main reason I was even considering a PSP is because of Grand Knights History. I saw a poster's avatar, did a reverse image search to figure out what it was from, and then looked up information and media for the game. It looks fantastic, and I'm interested enough that I'm willing to buy one of Sony's portable consoles for it. Something about Vanillaware titles really stimulates my inner J-phile, and GKH actually looks to have some substance to go with the lovely style. I've never really followed the PSP library very closely, but of the games I know, here's what else interests me:
God of War
Loco Roco
FF Dissidia (maybe, I've heard some generally negative things of the gameplay)
That yet to be released FF title Kagari made a thread for
That's all I can think of off the top of my head. I know there are a bunch of SRPGs that looked interesting back when they were released, but I don't know their titles or if they were even localized for North America. I'm fairly certain all of the games listed above are on PSN, but am fairly certain that physical copies go for less than what Sony asks. Now, I assume PSP Go is still supported and that a digital version of GKH will be released the same day as the physical copies, but perhaps I'm wrong here.
Also, whether I get the Vita First pack or just the console with a larger memory card is largely dependent on how big these PSP games get. I imagine some of these games will take up more than a GB? It seems like the 32GB is the way to go to be safe, but realistically I won't have more than 3-4 PSP games on the card when all's said and done, and for Vita games, I'll opt for physical copies unless Sony decides to charge less for digital.