The problem I find with plans is that they are 'one size fits all'. As a 49 year old woman, my training needs are going to be very different from a man in his twenties. I managed 3:50 at VLM this year, but did not follow a plan as I find I need to factor in recovery from my lsr. I agree that you need a mix of lsr, threshold and speed work, each week, but real life gets in there as well, so fit the runs in around everything else. Plans also do not take into account if you pick up a slight niggle and want to take it easy for a day or so to recover.
You could always try using one of your runs as a hill session. That should help. Also, cut back on housework, saves loads of time. I try and get away with the bare minimum, and get the kids to help out. That should release you for at least one extra run a week. Remember, your running serves as a fantastic example to your children, way more than hoovering.