I don't know if there are more or less this year, but I am definitely on alert for them because I encountered a nest in my garden just a few days ago. I'm fairly tolerant of them in general and much more tolerant of their venom than most people. Had it just been me I might have tagged the spot and let them be, but the girl here is allergic, and the cat likes to stick his foot in holes, so they had to go.
Your saying "they're kind of cuddly for murder-flies" is interesting because these were less aggressive than normal, I never thought about it being a time of year thing.
Maybe there are different strains of them because these were small, I thought at first they were hover flies attracted to where I had spilled water and even walked through them a couple times before they attacked. I'm tolerant anyway of bee venom but theirs was particularly mild, I don't know how many times they got me because they didn't enough of a swelling to count the individual spots. The pain lasted a minute or two and the itch, a couple of hours.
What to do when a yellow jacket nest is in your sweet potato patch? Pour gasoline or spray poison in the hole, ABSOLUTELY not! Shop vac can work, if your tolerant of a few stings, which I am but no extension cord long enough so I went in and got a big pot of water boiling, it worked a charm. Next day I dug to make sure I got them, rather than causing them to move and I found the nest and a much larger one which I guess is the queen. Now just the karmic debt for murdering the poor things in such an awful way.