I don't think it's fair to judge running surface alone when looking at impact and foot health. Realistically you are looking at the total package impacting your feet involving both the surface and your shoes. So for me I run in something like the Brooks T7 on grass and the Adidas Boston or Mizuno Wave Rider (Precision until they changed it) on the roads. Basically my foot feels about the same regardless of the surface I run on because I adjust the cushion/stack based on the hardness of the surface. Cushion on grass would be too soft for me and minimalism on road would be too hard for me. The result is that I find a happy medium on most of my runs regardless of surface alone.
My calf tightness historically has almost entirely to do with low heel offsets, soft heel cushioning, or too much arch support. Basically, calf tightness has to do with stretching on your Achilles tendon and the surrounding muscles, which has more to do with demands you put on its elasticity. Overuse and impact are obviously complicating factors and will be greatly magnified if running a 20 miler or sprinting 100 meters all out on pavement, but otherwise when it comes to acute injuries from daily moderate use I think elasticity demands are at the root of the problem.
Personally my calf injuries have always come from running on the roads. Often the main issue was wearing too low of an offset for what my calves can handle and I would have gotten away with it on plenty of grass running, but doing the same on road was not as forgiving. Running in Nike Free or ASICS Tarther on grass never really bothered me, but doing it on road quickly added up to problems. That variety of impact in grass makes it so the repetitive stresses differ slightly. On road your footstrike is unforgivingly the same with almost every single step and you lose that tiny bit of extra dampening the grass gives you as it compresses at impact.
My stress fractures have been in metatarsals and they have had to do with the bending in the metatarsals being a repetitive stress or sudden stress. My likelihood of getting the injury had a lot to do with how a given shoe delivers at toe-off and in that case too soft meant my metatarsal bent a lot and too little meant I had to do a lot of work in the metatarsal, so really I do best with just moderate cushion there (not too much or too little). Stress fractures vary widely depending on where you get them and I can see it being an impact force thing if it's happening in your tibia.