Have you ever heard about "periodization"? It basically breaks the year into different periods focusing on different things, like "endurance", "speed", etc. Instead of just repeating the last week for 20 weeks (wow!), it may be more advantageous and less boring to repeat a particular part of the overall program. Often people will do "Base-building" before starting a program, which just increases miles before focusing on anything else.

thanks, Afhill. I hadn't heard of that. I'm completely new to this running thing and have a lot to learn.