I'm through flying for 2018. I bought quite a few FCM fares this year; I found that often it was only $125-200 above cheap coach to get such fares on the return to the DC area from a western destination. I also used a number of RUCs and GUCs to get up front also. I would say that I was probably 55-60% for the year on those flights that I took a chance on.
I did not sit in regular Y the entire year; I never did worse than C+. The proof of this is that I still have 8 unused free drink e-chits in my Delta wallet.
While I had a number of flights where I got the last upgrade seat, the best upgrade of the year was ATL-SFO two Fridays ago, where I was
#3 for 1 F seat 40 minutes before departure; when I got to the gate the GIDS was showing that they had given my exit row seat away to someone else, and then the next flash showed that I was sitting in 1A. There were two no shows for F.