The main benefits of the PS4 versions are a constant 60 FPS (in very select areas this isn’t the case), 4K graphics on a Pro, all DLC is included (item and cosmetics DLC), extra English recorded audio from the Steam release and Japanese language tracks, and a turbo mode to double the speed of the game.
Truthfully you’ll be set with the Vita originals. I bought the PS4 versions because I wanted to play them on a console instead of a handheld, but after playing Cold Steel 1 on my PS4 I was hooked. To me they work better as a console game experience since I like playing a good long RPG on my TV, but the Vita version of 1 was a good time for as long as I had played it. I eventually bought the Vita versions since I found them for a good deal, and whenever I go on a trip they’ll make for good reading since Falcom games have tons and tons of text! Haha
If you like the Vita versions you can transfer your save data to the PS4 version (but not the other way around), so if you do end up getting the PS4 versions down the road you can make a copy of your saves and transfer them to the PS4 and play on there too.
So TL;DR - You’ll be just fine with the Vita versions. You won’t have access to some of the perks of the PS4 version, but the games are still very good on the Vita.