To paraphrase, collectability is in the eye of the beholder. I generally want (for collecting; obviously shooting is a different matter) only early four digit frames, and I want them in the configuration they left the factory if possible. But, if I ran across an early flatside frame only I'd snap it up if I could affort it.
Others might have different views, and it depends on what type of collection you want to put together. For example, if you want to assemble a collection of all the different frame/hammer/triggerguard variations you would need several frames. The earliest ones used a hammer that held in the hammer nose with a small lock ring at the rear of the hammer. The second ones used a small screw. Neither had any external safety, and the trigger guard on these contained no trigger stop screw and was a different shape than later ones. At some point, an external sliding safety bar was added to the hammer. Also, sometime in the 1970s the trigger guard and trigger changed shape and a trigger stop screw was added. Later yet, the "selector switch" style hammer came into being and the "easy open" frame was created. There were also stainless steel versions and Armour Alloy versions. Engraving patterns were changed several times. So, you see, to do this project you would need many different eras of frames right up to nearly the end of the original contender. You would also find yourself having to do quite a bit of research in order to determine just how many different variations there were.
So, there is probably no simple answer to your question without knowing what you want to accomplish.
RonF
