Hi Dave, I want to start off by saying value means different things depending on point of view; if you are selling, it is what someone will pay, and if you own something it is what it would cost to replace.
I have been chasing the 24' market closely over the last 12months and see what is on offer/people are paying. As of today, I know of 3 24' on sale; your rear-bath, another rear-bath on Craigslist in Portland at $4.5K (driving and having just completed a 100mile trip), and a rear-twin bed (eBay auction just ended, 8pm ET). The eBay unit is fully working, new Flexsteel seating, new flooring, and has a set of alloy wheels with good tires, and is a good case study. It was originally for sale on the classifieds here at $14K, then Craigslist at $12K. At that time (early this year) I was interested (before I got my 20') and exchanged emails with the seller. There were others for sale around $8K, and the seller was willing to let it go for around $10K but I bought the 20' instead. Since then he has had 3 eBay auctions (they come up on my daily searches). The first had an opening bid of $8K - he got no bids. The second had an opening bid of $6K, he got 24 bids up to around $6.5K, but never reached the reserve, so didn't sell. The latest auction had a had an opening bid of $7K and after a 6day auction had no bids.
This would seem to suggest the value was approx $6.5K (the maximum bid on the second auction), but then why would the only other unit I have seen for sale recently (a slightly later Airstream badged 1979) that has been up for sale for $20K at a dealer in Tulsa, disappear from the dealer inventory, so I assume sold?
As I say value is what someone will pay, or maybe someone needed to replace a 1979 and so it was worth more?