After looking at a YouTube review that really went in as to what changed, I can honestly say it's nothing relevant from our perspective... they compared the fps rates, which were exactly the same, and compared the resolutions it plays at which is also the same. They compared graphics and only seemed to find very slight differences in some foliage and shadows.
So this absolutely seems like a cash grab. I think you get some added modes or content, which is nice, but how or why would you call it a remake?
The only thing for me which is a notable improvement is the loading times. But when I'm playing through such a long game, what's another 50-60 seconds? Nice to have, sure, but not making me hand over cash to upgrade.
I was going to be all over this, especially as having the original PS4 disc edition gets me a cheap upgrade. But after watching the Digital Foundry video, I don't think it's actually worth it. Unless you really want the bonus material, get the original cheap and let it apply the PS5 patch.