I can chime in here based purely on my experience. I am not fast, my marathon PR is 4:33 at Marine Corps, but here goes...
I have run six marathons to date, the first couple were in the 5:00 neighborhood. I was basing all of my training on plans copied out of Runner's World. After my second marathon I started using an intermediate training plan that included speed intervals ranging from 200's to 1600's, particularly what they called Yasso 800's. My running improved dramatically. Then for some idiotic reason (probably weather related) I started doing them on a treadmill. Good workout, but not nearly the same. I would love to go back to the track for this and to learn pacing - something I struggle with constantly. I would also welcome the opportunity to get some tips on form and drills to help me get off my heel strike and get better at midfoot or forefoot running.
Now, for motivation, not sure if just a beer would do. I would need someone carrying a big plate of slow-cooked ribs or pulled pork, or a plate of veal osso bucco on a bed of fusilli. But that's just me...