FWIW, I had cruddy seats in the back of the plane for my intra-Europe flight on a reward ticket last month. At check-in I spent about 10 minutes convincing them that as a ST E+ I got lounge access. Much to my surprise at the gate we were upgraded to Tempo Challenge class. I'm not 100% sure what the upgrade included, other than seats at the front of the plane, as I don't know what the service was in the back. We did get a meal and free booze, too. And we definitely couldn't get seat assignments in advance for that segment since it was intra-Europe, in line with COFan's comment above.