I have a '92 D-55 and a '76 D-50. They have very different tones... My 55 has a rich and "majestic" tone. My D-50 is louder, much more "in your face." It's a bit "brighter" and brasher sounding, with great bass, stronger mids than the D-55, and more sparkle to the trebles. I like them both for fingerpicking, but for different tunes. If I am going to be strumming (cowboy tunes) with a pick, I reach for the 50. I'd bet bluegrass players would love it (BTW... a '70s D-50 will have a Sitka spruce top... adirondack/red spruce wasn't introduced until production moved to Tacoma; I thnk all 55s are Sitka).
Pricewise, I agree that $1600 is a steep for a private sale, tho' that is within (at the high end) the range you will see in shops. A year ago, eBay prices for D-50s from the '70s-early '80s in decent condition ranged around $1000-$1500, depending on condition. They often sold for a higher price than a DV-52, and even outpriced some D-55s from the same era. Prices on D-50s seem to have dropped abit recently, and I have seem them sell in the $800-1000 range. Mine, which I got for ~$1K, was in EC, with the exception of a hairline split between the bridge pin holes... now repaired to near invisibility.
Dave