Charging for upgrades would go over so much better if a row was pulled out of economy and the space added to just five rows for Medallions. On United I don't even bother upgrading half the time. Middle seats blocked, 36" pitch.
There are a few choice seats that are far more comfortable than FC. Last week flying ORD-SAN in a 757 I traded my upgrade for the second exit row in a 757 when the agent said he'd block the middle. 17 on a 757 and 6 on Airbuses to name a couple.