I've been working on getting my running speeds up too this year. Two suggestions:
Replace one of your 30 minute sessions with a longer run, at least once per week. A long run meaning around 1.5 hours.
On the intervals, push yourself on max speed every time. Try to get the max speed up.
Pick up a copy of the Hansons Half-Marathon Method. It's pretty good at describing ways to get your speed up.