Interesting perspective, articulately expressed as usual Bob. I certainly did not respond with the notion of passionate that you express; on an needle to eye basis I would say none since none of these would have much appeal to me if I couldn't see them. Rather I took the term as one of its alternative definitions provides "...expressing, showing, or marked by intense or strong feeling...". Now in context, I think you can have an intense or strong feeling about any collection you intend to continue or expand; if you do not, why are you expanding it? Thus if you only acquired a couple of figures for a period or only dabble in it from time to time, it would not be included. But if you intend to represent multiple or signficant aspects of a period and enjoy learning about the history that relates to it, then I think it could be. I know I wouldn't have a 100 or so of anything unless it met my definition of passionate.
It is interesting how interpations can vary on that score.
You are undoubtedly right that a poll was not needed to know that WWII was decidedly the most popular here but I have found it interesting to see what other members are "strongly interested" in collecting besides those things mentioned in their usual posts. I guess one man's treasure is another man's trash; which is how Ebay got started I suppose.