A very impressive collection indeed!
I actually am a bit of a collector anorak myself! I've always kept all of my sims in original boxes with manuals and last year I had some spare cash floating around (if only I'd kept it - doh!) and I went through the entire listing at http://www.migman.com and bought "as new" copies of every combat and civil sim from 1988 - 2005, I actually have a double wardrobe 8 feet high, 6 feet wide and with 5 tiers inside filled with Flightsims and associated addons. I never really went much for scenery but have every stand alone sim as far as I'm aware and, yep, you guessed it, CFS1 is the only incomplete in my collection! you can imagine my frustration!
P.S - I beat your FS4 as I have back to FSII on what looks like a big VHS Tape! with 8 diskettes with scenery areas! some of them still in packaging, date on this is 1982.
Its worth noting that some of the older sims, especially the "Janes" collections are actually worth quite a lot of money. A good copy of Janes F-15 or Fighter anthology in box will regularly fetch £50 - £70 on eBay. Falcon 4 with all the manuals will also get up to £50 although with the newer version released last year this has gone down strangely.