I can tell you that once I had the diagnosis that my nerves are in fact damage, my condition is taken much more seriously as far as getting pain meds and seeing specialists to run tests to help me find a cause.
If you already have a diagnosis of RA, you have autoimmune activity going on, so the biopsy and small fiber nerve damage might get you IVIG.
I would say that if you have extreme pain levels, that the diagnosis would be useful for getting an arsenal of pain meds and muscle relaxers for flares to keep you out of the ER. If you already have all this covered, then I don't see a point in the biopsy.
I had one from my ankle and one from my thigh. It is over very quickly and nothing compared to an EMG or a sjogrens lip biopsy.