The 586-4s chambered for the 38 Special are over-runs from contract with Brazil for one of their police agencies. The were made in 6", 4" and 2-/12" versions. There is varying information on how many of each were produced but there weren't a lot of them.
Value is pretty much what someone will pay for them. Some folks think anything of limited production should be worth more, while others think being limited to 38 Special only is a strike against them.
I have a 4" and a 6" and treat them like modern day versions of the old 38/44 Heavy Duty or Outdoorsman. I shoot my with hand loads duplicating the old 38/44 performance (158g @ 1150 fps) and they are a delight on the range. More powerful than 38 +P but more controllable than full blown 357 Mags.
Dave