Is it worth upgrading to an SSD?

[Diesel]

There’s a limit to how much faster things will be from the game/system side despite the potentially much faster SSD speeds, but it is definitely a noticeable upgrade playing PS4 games from an SSD than a standard HDD. The loading times on something like Horizon Zero Dawn are significantly improved in my experience.

And as mentioned above, when you get a PS5/Pro you can slap the 2TB SSD into an enclosure and use it for all your PS4 games as an external to maximize space on the PS5 internal SSD. It can also be used to store PS5 games (but not play). Moving them back and forth is relatively quick.