Buy Xbox One X if you already have an Xbox One S Special Edition Is it worth it?

Is it worth it or should you stay with S are still the same games!

There's no general answer to this. The decision is solely based on your personal circumstances and interests.

In contrast, the successor is already in the starting blocks and is also downward compatible. It is also relatively expensive and the advantages are more of a technical nature, since, as you say, the games are the same.

However, there are also some indications that you have a reasonable 4k HDR TV. On such a one you can already see serious differences. Many games also benefit from more or more stable frames. The foresight is higher or distant objects and their details are more visible.

I myself have a One X and a PS4 pro. Both are connected to a Samsung Q7 with 55 inches. When comparing in World of Tanks with identical image settings, you can clearly see that the One X is ahead.

Hope this helps you a little with your decision.