I am an 800 meter runner who PR'ed off of 30 mpw and no real speed training this past winter. I did lots of strength and hill work -- 800 meter repeats on the track, tempo runs, and lots of hill repeats. I ran a 3 second PR in the 800 doing nothing shorter than a 400m repeat in practice. (I also live in New England where it is difficult to train outdoors in the winter.)
I am also doing base training right now -- 40-45 mpw, lots of long intervals, a medium long run,and a long run. I am looking to peak in May / June. My coach had me start doing 5 x 100 meter strides with a 25 second recovery both before and after workouts (twice per week) weather permitting. I also do drills and short but fast strides / form work 4 days per week, and I lift twice per week.
I found that doing the longer stuff made me strong. I actually almost hit my 400 PR indoors off of no speedwork and my PR is pretty decent for an 800 runner. What I've found is that unless you are blessed with elite level 400 speed, you have to be strong enough to hold the pace you want for the entire 800. Otherwise you will just die after 600, which I've done and it's not fun....