This is how I felt. When it comes to P5, it feels pretty complete as-is. As a general rule, when a JRPG re-releases with extra stuff, the new content frequently doesn't mesh organically with the original vision. Like you said, P5 was 100 hours on its own, and it's not easy to restart the same story from the very beginning just for some extra dialog and characters.
Now, if Xenogears had gotten a director's cut back in the 90's or early 2000's, that would have been a different story.
That reminds me, I stopped playing vanilla Dragon Quest XI at about the half-way point, and I'm still debating if I should switch over to the Definitive Edition for those extra bits. It's hard to throw 30 hours of gametime away, and fans have told me I'm not missing much.