I would take the position that this is a genuine, legitimate tsuba. The quality may be comparable to Nagoya work, but I think it is nevertheless a rather mediocre piece from the late Edo period, and definitely not a modern reproduction.
The file marks on the nakago and hitsu-ana also look natural to me. Even on more expensive pieces, these areas were not always polished completely. If you look closely at the actual workmanship, you can see that the nanako was made with a hand tool: there are many sharp sections between the individual “dots,” and the tool marks are clearly visible. With casting, all those fine, sharp details tend to become smoothed out.
As for the gilding, for some reason everyone seems to think that it should be perfectly even and uniform, especially on simpler pieces. That is not necessarily the case. Applying gold amalgam with perfect precision and evenness is not easy to begin with, and during the heating/firing process it has a tendency to spread beyond the boundaries that were originally defined.
This photo is revealing to me.