Is it worth it or would I be better off with the Roku (or spending the extra $ on the newest Apple TV)?
If you are happy with the Roku, I would just stick with that.
I personally think that the Apple TV and tvOS has the best UI of the streaming boxes, and even at 4 years old, the ATV4K1 with the A10X is still faster than the chips of the competition.
That said, once in the streaming apps, there really isn't any obvious difference between tvOS and the competition.
The ATV would probably be faster, but not worth it for the extra money if you are happy with your current Roku.
Right now, the Apple TV has potential but it is basically an overpowered, and overpriced steaming box.
FWIW, I would use it for streaming only... not games.
This is where the Apple TV would have an advantage, but even for games, there has been a mass exodus for tvOS gaming developers.
Many gaming developers are dropping support for tvOS, while continuing support and updating iOS and iPad OS version of apps.