Good thread and great posts here. Strange enough, I am doing the same (30ish mpw, only 4 quality runs per week due to work and family). Keep on the effort. I like the idea of running hard tempos (4 miles), rest, 4x150/200 (800m pace) or 8-10 strides as one of your weekly workouts.
8x400 at mile pace is a very good workout and absolutely enough for 30ish mpw. Stick to it regularly, but be careful. Stuff like this is taxing and might ruin the whole season, if done too hard and too early. Consider variations, be honest to yourself and build it up carefully. Make it just a little bit harder every week or every other week and make sure that you run all quarters at actual race pace, not goal pace. All quarters should be in the same range. A few suggestions, it is up to you:
- reduce the rest step by step (week 1: 90 sec, week 2: less...)
- standing rest first, after a few weeks active rest (jog)
- 2 sets of 4x400, later on all quarters in a row
- start a few quarters slower than mile pace, but finish a little bit faster for developing a good kick.
Whatever you do, increase the quality but do not race your workouts because the whole week counts and not a single workout. At the end of your build up (perhaps 6 weeks?) you should be able to get in a 1200m time trial at mile pace or 8x400/60-70s rest. Good luck!