Here's what I posted in another thread back in 2013:

"You never know! When I was in South America recently I had 7 or 8 internal flights, all on Star Alliance airlines, all in economy. On the first flight I asked if an upgrade was available and noted I was Star Alliance Gold. My intention was to pay if it was not too expensive. Got it for free for myself and my wife. After that I proceeded to ask on every other flight (except for 2 where I was already upgraded at check in). Got it on all but 1 and remarkably, only had to pay for one, from Lima to Bogota. Coincidentally this was only 1 of 2 flights where I had to ask at the gate (the other one I asked for at the gate was also denied). For the others, I asked at check in. Quite frankly, I was amazed by this.

Motto: Never hurts to ask!

I think I went from Lima to Cusco (ug) to Puerto Maldonado (ug) to Cusco (ug) to Lima (ug) to Bogota (pd ug) to Quito (no) to Baltra (op up) to Quito (op up). Of course I attributed all my luck to experience gained on FT and the short holidays/mileage runs or bizarre routings I've taken over the years to maintain status. Mrs. Allbrosca said she would never bother me about it again "