I tried to do this last month. I could buy a US$1500 SYD----MVD flight in economy, but if I wanted to buy an economy ticket with flights where upgrades were available, the cost was around US$3500. I ended up paying US$3800 on Aerolineas Argentinas for a discounted business class seat instead. And the flight time was around 18hours faster also. So sometimes it is a false economy trying to upgrade.
I can understand your post but it does not address what the OP asked. Most people trying to upgrade do not want to, or cannot, pay $3000 to $4000 for a ticket. Many people would simply see what flights upgrades are available on on book that. Or they would resign themselves to being in coach. That is why i said that upgrades were capacity controled on AA.