Couldn't resist a quick reply. Exercise is always good, however, with SFN it just seems to make it worse or add additional symptoms. It may be just my case, but the normal numbness, tingling in my hands becomes an additional burning sensation after playing a round of golf or working in the garden. The studies you refer to certainly didn't include me, but they were probably geared toward leg neuropathy where blood circulation is usually a contributor. Exercise in this case would certainly be healthier for the patient. On a side note, I have heard that nerves are not nourished directly through the blood supply, but better blood circulation may increase the exposure of the nerves to the nutrients they need.
Good luck in your continued research.