As a 1K last year I found fare class to have a large effect on where I was on the upgrade list. On a YBM fare I would often be near the top. On an S fare I might be 15 on the list.

I was on more than 30 flights where I had a YBM fare and didn't get upgraded though. On many, first class was sold out. On others they up-sold first until it was full.

Next Sunday I am flying to EWR on a $700 one-way M fare and I have a center seat in coach. First and e+ are completely sold out.

My travel is at peak times, often between hubs, and I often buy First because I don't expect to get upgraded.