My upg rate is way down YoY. I'm at about 40% this year, was about 65% last year. I'm even having issues finding C+ seats. I'm sure where/when peeps fly makes a difference. I book typically 3-4 days out, usually on a Monday-Thursday itin. This year already I've seen more middle seats than the last 9yrs combined.
I suspect that over the last few years, DL's seen a big influx of FF's from other carriers (for many reasons). I think that's leading to issues where we see 80+ peeps on an upgrade list for an MD-88 flight. I've considered a switch to UA, since they are maybe the only U.S. carrier adding F/C+ capacity. Right now, it would be a pain as they only serve hubs from RDU (and don't have a club).