I always say if the marathon is a part-time interest, you will only get part-time results.
If you want to win a race you have to go a little berserk.
Being a runner means you are now 'free' to win and lose and live life to its fullest.
Aiming for the marathon is a task of sorts which can include terrific highs and lows.
I believe you'll develop speed via strength work which includes hill running, either repeats, or running hilly courses as the Kenyans do on a steady basis
Hills are terrific for running