I have never been able to work my way into having abs. I was a stocky fellow in high school walking around between 175-185 at 5'9" and I was in good shape and very strong. But for me its all about diet. I'm in fat mode currently weighing about 168ish but if I wanted my ab definition back I'd go clean for a couple months down to 155-158ish. i wouldnt even touch my workout routine.
I'm pretty much in the same boat as you, though i've not really been above 165. I;ve always been in relatively good shape, but the last few years i kinda let myself get a little wobbly
I've only recently (the past 12 months or so) looked at changing my diet from pretty much being able to eat anything, to eating healthy. I think my metabolism slowed down somewhere during my lay off period!
So what would you suggest? Quit the weights, plyos and resistance training and do intense cardio for a couple of months? Maybe a little core exercise here and there but little to no lifting etc?