I'm in my mid-30s, and regularly run about 50 mpw.
I also walk my dog a lot, walk to and from work everyday, and walk to the grocery store, library, etc. averaging 4-5 miles a day. For me personally, walking is a big help. I don't think I gain a lot extra aerobic benefits, but I think it really aids in my recovery (both physical and mental). I have noticed it most in periods when I up my mileage or intensity. Things get sore or tight, but 20 to 40 minutes of walking always leaves me feeling better.
I think it could help most runners out IF they like the idea of walking. I really love walking, so of course I find it helpful. But if you can't stand going for 20 or 30 minute walks in the evening, it won't help you.
But give it a try for a month or two. See how you feel.