I've been running pretty consistently (at least 3x per week) for about the last 4 yrs. I've never really done anything above a 10k, with the exception of 1 1/2 mary. I pr'd a year ago in the 5k with an 18:30 and ran a 10k in 39:47, two weeks later. Since then I haven't been able to go below a 19 and 40:25. That's just cuz its more of a social thing for me now, I have a running partner I get along with really well, and hes had a struggle to go any faster, and I'm not gonna leave him.
I alternate my shoes between the New Balance 805 and the 903. Both super lightweight and really narrow with a relatively tight toe box. They're not shoes I'd recommend for the majority of people,as they are so light and don't offer a whole lot of support, but I can get away with it because of my build( i'm 5'10 and only weigh 145 lbs.)
And as said before the best way to increase speed is to vary your workout. For me personally I have one long run a week ~ 13-15k, a tempo run of somewhere around 8k, and intervals, which i typically do as fartleks, or hill repeats.
If I wasn't able to run, I think I'd be a whole lot more stressed with my life, as it seems to be something always keeps me really level
