Whether it is worth upgrading is probably a very subjective question that nobody will be able to answer for you. Depends on what you're after. If you just wish to check out the current version's user interface, core engine and in-app store system/content, there's a completely free version of that on the website. As far as the paid-for editions go, maybe the following comparison table comes in handy:
Since soundpool content seems to be your main focus, this table will show you how many soundpool credits you can get from the Premium and Plus versions. If you compare this to the price of the individual soundpools in the in-app store, you'll see that the editions are a good value-for-money option. Naturally, if you're strictly interested in audio loops, there are also many dedicated third-party producers of content that will work with Music Maker (via standard audio file types like MP3 or WAV) that you can consider. The handling of those third-party loop libraries just won't be quite as convenient as the handling of MAGIX soundpools via the soundpool database/manager.
If that's really version 16 (as opposed to 2016), it's also pretty old, and you might find it hard to make this work properly under Windows 10. So, this alone might be worth an upgrade.