It sounds like you have a pretty good system in place, but I'll take a shot at answering this. 57 year old male, ran 3:04:42 last year September, just ran 3:16 last week coming out of low mileage winter period, but was 1:31:45 at halfway, so I'm in the pace neighborhood you're looking at.
For me, running 10 or more miles at goal pace every week becomes a trap, where I end up "racing my workouts" trying to set course records. Many schedules will have you run longer, like 12-15, but with the last 6-8 at goal pace. Vary your pace workouts; don't get in a rut.
At my age, I've evolved to a more relaxed approach, often running trails and not worrying about pace per mile. For me, the total volume of aerobic training in the 6 months prior (including cycling in my case, as I'm primarily focused on triathlons) is more important than the "hard" workouts. If I can run 40-50 per week along with cycling 100-200 miles, and have a long run of 18 or more every 10 to 14 days, I'm ready to run between 3;00 and 3;10.
But you asked about speed training. Last summer, the only speed training I did was when I would bike home from work, hop off the bike, and go right into a run to practice my transitions for triathlons. I would often do a 2 mile run, gradually accelerating from 7;00 pace at the start to about 6:15 pace at the end, focused on smooth running form, not all-out speed.
But perhaps when I do hard bike rides and really push on the uphills, I'm getting the kind of heart workout you would get from sets of repeat miles or 800s. I guess I'm just suggesting that the marathon is a different animal than the 5k-10k- half marathon. For those races, sets of repeat miles or 800s, with progressively shorter rest intervals, will help you prepare to bash all the way through the race on your red line (anaerobic threshold). But for the marathon, you'll be running maybe 20 seconds per mile slower than threshold. While that kind of high volume of repetition training will improve your fitness and make your A.T. pace faster so you can theoretically have a faster marathon pace, too, I think it's not as important or even desirable for the marathon, that maybe smaller doses of speed work can suffice.
Just one man's experience. And who's to say I wouldn't be running faster if I did more workouts like 6 X one mile in 6:30?
Good luck.