Well, there are Star Alliance upgrade rewards, not sure if A3 offers them or what the mileage amounts are but they are usually reserved for highest paid fares - B,Y, which people usually don't purchase.

Furthermore, I've tried getting an Economy Plus seat assigned to me based on my Star Alliance Gold status in the past but I've been told - sorry, it is not our policy to provide that benefit free of charge for Star Alliance Gold members. That's happened to me at both the gate and at an United Club. I haven't asked for first class but I'm guessing if I did, they would have laughed at me. The reason I even bothered in the first place is because United provides their Silves and thus, Star Alliance Silver members access to Economy Plus seating on day of travel free of charge, so I couldn't understand why I as a Star Alliance Gold am not allowed but when I complained to United about it, I got no answer.

You can always hope for an upgrade offer at check-in - whether online or at the airport. That will be your best bet to travel in anything else besides economy.