In my opinion 70 miles sounds like alot for a guy who does 2:40 for 800, (and maybe 17:30 for 5k?). My guess(correct me if im wrong) is alot of that is just jogging, and i think you need more serious workouts to in order to reap the benefits of the great base you probably have from all that milleage.
But I don't necceserely think those workouts must be speed workouts, i think they should be more like workouts at 3k-10k speed, and speed workouts just once in a while. And i think that because if you do workouts at 800m speed, you train the anaerobic system instead of the aerobic, but you could still benefit from some speed training because you train your legstrength and coordination, etc. resulting most importantly in better running teqnicue.
Ofcourse you can never run 5k faster than you can run 800m, but that doesn't mean you need to train 800m speed to get faster 5k, rather i think it means if you have very close paces in 800m and 5k, training for 5k will make you better at 800m, rather than the other way around.
Also some tempo workouts would be good. But all of this depends alot on what type of runner you are aswell. One way that i used to train before that i feel is pretty good for having gurranteed decent training(but probably far from perfect) is like putting something of everything. Like doing 2 workouts a week+ a long run, with over 2 weeks ex. 1 workout @400-1500m speed, 2 workouts @1500-10k speed and 1 workout @10k-marathon speed. Like i said, almost gurranteed decent results. And finaly make sure you don't overtrain!