In reply to TheDrunkenBakers:
General strength traing helps with most things but depends on how much it cuts into your running. Periodizing would be a good idea, with cycling strength training.
Doesnt need to add weight at all, but serious gains requires rest that will reduce your running time, likewise big runs will interfere with strength schedules.
Maybe 2 or 3 strength phases per year with regular but minimal maintenance and accepting some loss.
Leg conditioning will help, but thats more than just about strength. Id include plyometric, ROM, stress and back of leg work too.