I was at a college back in the day and we normally ran 75-80miles a week evenly split between dirt roads, hiking trails (some in good shape, some in not so good shape), intervals on grass (during fall) and on track (during spring or just faster stuff), and asphalt/concrete around town. But we also did pool workouts a couple times a week to 'get off our feet' and do high quality aerobic recovery work without the pounding. Of course we also soaked in cold water streams 3-4x a week after hard sessions and long runs (gotta love the mountains for that). Based off that my two cents would be it's really in how you recover. Maybe harder surfaces can be utilized more, but just make sure you take extra steps to recover. Little extra stretching here, little more protein there, etc..
I think variety is key. There were times when I trained exclusively on asphalt simply because I didn't have access to trails/grass, etc. Body adapted with proper shoes, but it also wore the shoes out faster. I was slightly injured more from training on harder surfaces, so my last couple of years I moved mainly to trails/grass for long runs and only used asphalt/roads for morning runs on 2-a-days or just when I couldn't make it to the local park. Stayed healthy and injury free for five/six months and noticed I recovered better. But, again, probably variety as much as anything helps.