Both the Persona 3 Portable remaster and SMT3 remaster were disappointing to me, unfortunately.
After numerous attempts in trying to play the Persona series, I realized that the series is just not for me. That said, the remaster of Portable felt like it was an inferior release when compared to the PSP original, with worse audio and lazily applied upscaling.
SMT3 is a game that I rather enjoy on PS2, as I have found its atmosphere and gameplay to be well-done and engaging. The remaster on modern systems felt less stable when compared to the original. To deal with the cutscenes still being in 4:3, compressed audio, and performance issues all the while being charged around the same price as a modern AAA title was very disappointing for me.
The game has been patched as far as I'm aware, and is probably more worthwhile when on a deep sale simply because at the end of the day SMT3 is a great game, however I still regret buying the game before a significant discount.
In the case of both of these releases, it still appears that their original incarnations are the preferred way to play (without taking into account the whole "best P3 version" debacle, of course).