The adjustable sight models were also used for Metallic Silhouette matches, allowing the sight to be set for the four distances. The stainless steel 686 variant is not uncommon, I've never seen a 586 AFS.
That being said, it is not a collectable in the sense of age, rarity, workmanship or value; its just a fine firearm that can be shot with heavy .357 Magnum loads without developing premature wear.
A second hand K frame Model 19 or 66 can be had in a six inch barrel without the full under-lug and use the same grips as the 586. It will not handle constant .357 magnums, the 586 was developed as a slightly heavier, larger gun because the Model 19 could crack its forcing cone with high speed light weight magnums. You will not find a factory patridge front sight on a regular production 19 or 66.
The K frame Model 14 K38 Target Masterpiece in .38 special did come with a patridge front sight.
The .357 Magnum Model 27 N frame is larger, does not have a full under-lug, will balance closer to the hand, can handle constant .357 magnums and can sometimes be found with a patridge front sight.