Dan I also race from 10k to 1/2 Marathon distances and follow the following program which has knocked 6 minutes off of my PB for 10k in less than a year!
Mon-10-15 miles easy(road)
Tue-6-8 miles easy(week 1 off-road,week 2 road).
Wed-7-miles,1 mile steady then continue with 3 mins fast/4mins steady (no jog)
Thu-7-10 miles easy (week 1 road,week2 off road)
Fri-1 mile easy then strides/skipping/bounding:- (week 1)3x1 mile(3 mins rest between each)
(week 2)5x1000m (2 mins rest between each)
(week 3)6x800m (1 1/2 mins rest between each)
(week 4)12x 400m (1 mins rest between each)
Sat-Rest
Sun Race or Fast run/time trial (5miles/10k)