I think I can safely say that those who have it find it worth it. Otherwise they wouldn't have it.
Also the Supporter package gets expanded constantly, meaning the package will get bigger and more interesting over time.
It most certainly is a good addition to the game if you like to spend some time in it.
You do not get any advantage over non-supporter players however, because that would not be right, but certain info is easier to access, where others need to use other tools to keep track, for instance with the bookmarks...
Therefor you get no trainingminutes for PL games, nor will injuries stick.
If you didn't already, you could read the supporter part in the rules which gives you a nice overview of what you will get for the money.
One of the features that didn't interest me at first, but after a while is one of my favorites is the out of town scoreboard.
You can see other's games in the header of the page and when my game has finished I often see a nailbiter with a few minutes left, so I can click on it and instantly follow the end of that game, which brought me some real exiting moments already, often more exiting then my own game, especially when it matters who will eventually win it...
They are not your friends; they dispise you. I am the only one you can count on. Trust me.