In my area, (assuming the tires are good to excellent, and brakes & gears are all dialed in and working properly) I would list in on Craigslist and FB marketplace, and start out asking $150 and figure on selling it for $100 - $125. I would certainly not bother putting a bike like this on ebay and have to pay the fees, ship it, etc.
There may be a very limited collector market for it, (like almost non-existent, especially with it being a girls bike) and so, it is generally not considered a collectible bike. However, bikes like this make excellent every day riders, and are much better quality than the junk that walmart sells.
As for the year, I would agree, late 60s to early 70s. I do not know of a way to nail down an exact year for it.