By the time I was a cat 3 the group rides stopped being challenging, but I kept doing them because it was the only way I could stay motivated to do bigger hours. But If I ride off the front, the group behind blows up. Kind of a dick way to get fitness around here. If I had some proper group rides, maybe I'd consider differently. Now my only group rides are much smaller with guys that will ride similar to the way I ride, but they're also less frequent. If I go to a Tues/Thurs/Sun ride and ride even a bit above threshold for more than a minute or two I'll be by myself pretty quickly. We just don't have the depth or quality of riders where I live and rides are simply too slow.
So I just do mostly workouts on my own rides where I don't have to stop pedaling. So anyway, to the point, my last few years of 8-12 hours is getting me more quality than 20-25 hours used to get me, which is important at this point when I have no time nor desire to ride longer.
I don't know how trainer workouts came into the mix, but I don't have to bother with those other than a month or two in the winter, so I don't. Can never get nearly the same effort levels or motivation on that.