tomgdaly, RacerEx knows far more about this than me, but FWIW here's a perspective on your schedule from someone nearer your own class.
I'm just a year older than you and in my first season racing, also as a Cat4, here in the UK. I haven't gone in for the veterans/masters stuff because, frankly, most of the old guys are faster than the new young guys and some of them are still racing at a very high level. At least I know that most of the Cat4s aren't very good!
Anyway, I'm surprised that you report being overtired with the regime you describe. I spend about twice as long on the bike as you do - 12 to 15 hours in a typical week - and feel reasonably fresh most of the time. The big difference seems to be that most of my time is spent at a lower intensity, with much less time spent actually racing. I might race one crit in a week, rather than a crit, a TT and a RR, which is what I understand from your programme.
So, I would typically have one long ride of around five hours, mostly in zone 2 but pushing it a bit in the hills to build in some intensity. I'll do one session of a couple of hours at tempo and one interval session of an hour or so. On the intervening days I'll be on the bike for a couple of hours each day in Z1 and Z2, pretty much recovery pace. if I have a race on Saturday I'll make Thursday a recovery ride and take Friday off.
That's roughly the usual routine, anyway. I'm not as scientific as I might be with regard to easy weeks, I tend to just ease up if I start feeling jaded. Reading what you say leads me to wonder whether your base is as well-established as you think it is? Maybe you need more long steady distance stuff before doing three really intense efforts per week?