There are some things in this world that you can't have too many of. Take electronic flashes, or Speedlights, as Nikon calls them. I will admit that Joe McNally is my hero in this regard. He often creates incredible photographs using a dozen or more Nikon speedlights, placed singly or in groups, to achieve spectacular lighting effects. Remember that phrase, "in groups", as this was my reason for accumulating the dozens of speedlights I now own.
If you're wondering about the two silver pins just below the red face plate, they are two of the three contacts that connect the flash to the Nikon SD-8 or SD-8A supplementary battery pack. The contacts are normally covered by a plastic cover plate. I assume that the former owner used one of these power sources because the plate was missing when I bought it. No great loss.
Another Nikon Speedlight to consider is the SB-80. When in manual mode, the output can be reduced to 1/128th of full power. It too has a built in slave and an external PC port. It is smaller than the SB-26, and appears to have the same body dimensions as the now discontinued SB-800. This will make it easier to fit the Lumiquest CTO filters that you'll eventually want to get. It too is overpriced, just like the SB-26.