I have always ridden ladies bikes and often found them to be a better ride. Infact if you have to go up a hill on a mens bike it sucks - they are so horrible to ride - you are standing on the pedals the whole damn time. I use them on flat. Ladies bikes are much better geared - you can remain seated. I never even thought twice if it was a mens or ladies bike I was riding. My first 2 cool bikes were ladies bikes and I never even for one second thought I'd look silly on them or something. That is reserved for guys who are still stuck in the whole construct of what it is to be male - a purely cultural contruct that hearkens back to the days of the macho guy and the little giggling girlies. Those times are passed and if you don't feel right riding a ladies bike for purely gender reasons then you are a dinosaur by today's standard and you probably lived in the countryside all your life where things are often behind the times.
Mens bikes are worth more because dinosaurs still exist but also and probably more so because they are harder to get since there are less of them.
I grew up in London and used a bike my whole life to get around and nobody ever thought twice if they were riding a mens or ladies bike. In general people prefer ladies bikes if they are old because in Europe the ladies bikes are so much cooler than the typical diamond frame mens bikes. In the US the bikes are just cooler full stop. Including the mens bikes. But in the end I'd say they are about equal. My most recent pair of bikes - I like pairs - not singles - shows exactly that the ladies is totally as cool as the mens, but they are both cool bikes.
The fact the girls bikes are cheaper and in better shape and easier to find is a total plus for me because I like them just as much as all of them.
Everywhere else in the world they are worth the same. It's just the US and not even Canada where it's like this. There are way more enthusiasts than collectors anyway - surely enthusiasts drive the prices. It's only seasoned collectors who have this view on things, including myself, but if it wasn't for us who know exactly why boys bikes in the US are worth more, then it would simply be a matter of taste and I would guest that the simple enthusiasts don't have the same prejudices unless of course they are dinosaurs.