I think the thing is, what works is the group thing.
Running sucks for the most part. Getting beat sucks more.
When I have been running my best, it's when i work out fairly regularly (but not every day) with a group, and I find myself doing my damnedest to not get beat, and to whup on somebody in front of me.
Then, on the off days, I was busy doing what i needed to do so i would be even more competitive the next time we were going to get together.
I think that's just human nature.
Maybe putting yourself in that kind of environment a couple of days per week might help.