"I call the airline and say I would like to use 20,000 miles and up grade"
I was warned about this many years ago when flying for business. I would never call them up for upgrade, always take my chance and do it at the airport.
I went to South Africa 5 years ago and upgraded on the way out for both ways. On the way back they had no business class available and I got first class. That was South African Airways and they had the proper bed seats in those days.

Nowadays, coming to LV, I wouldnt bother using miles or money on an upgrade if it wasnt free. My flight from here is daytime all the way and after 2 weeks doing 2500 miles in Nevada Im so shagged I could sleep anywhere
Ive had good luck in economy also though. Last returning trip I got an emergency exit seat with the one next to me vacant, and last November on the way back there was a row of 4 at the back empty as the TV screens weren't working so I just laid down across all 4.