I could make a new category (General Category, WW&F Railway Museum Discussion, The Original WW&F, Other Maine Two Foot Gauges, Worldwide Two Foot Gauges, and Other Narrow Gauge are the existing categories) called Archived Discussion Posts and then split it up in there into sections.
Or, I could add a new section for each category. For example, in WW&F Railway Museum Discussion, we already have Museum Discussion, Volunteers, and Work and Events. I would add a fourth section, Archived Discussion Posts that would contain all the old posts in all of the sections in that category.
Regardless, if someone replies to an old post, I'll move it into the active area.
The first option is slightly easier. The second option is (probably) more functionally useful.
I've got a busy schedule for the next few days - so any change will come at the end of this week.