The nine-day cycle is pretty common, and for exactly the reason you cite. For older or injury-prone runners, it makes a lot of sense to have two recovery days after hard-effort days. There are a few of us on the 50+ training and racing thread scheduling the nine-day cycle.
Earlier this year, I experimented with a variation with just one recovery day after harder efforts. It looked like this:
Long run
Recovery
Recovery
Lactate threshold workout
Recovery
Secondary long run
Recovery
VO2max repeats
Recovery
Long run was 12 to 20 miles, at somewhat slower than marathon pace. Secondary long run was 12 to 14 miles at closer to marathon pace.
But I gave myself the option of just going easy for the long runs if necessary.
LT workouts were long repeats with short rest, or continuous tempo runs. VO2max repeats were 6 x 800m, 3 x 1600m , or 3-minute hill repeats.
I was targeting a half marathon, but with the VO2max work I felt just about race-ready for shorter stuff, too. In fact, I set an "age-graded" 5K PR during that training cycle. And ran my goal time for the half marathon.
My current goal is a marathon, so the cycle is: Long run, easy, easy, Secondary long run, easy, easy, Lactate threshold, easy, easy. Some VO2max repeats later in the macrocycle (based roughly on Pfitzinger Advanced Marathoning plan).