Dude,
I lived in Shanghai for about 1 year, in 2003. So I am afraid my info is a little bit outdated for your needs. However, I guess I can comment on Shanghai on more general terms, someone should, since other people haven't done so yet.
I think you are right and wrong at the same time. Yes, Shanghai sure as hell ain't no Bankok or Amsterdam. Chinese people are very concerned with appearances and cultivating the morally superior image is still quite crucial, even in Shanghai. That is my impression at least.
Still, mongering is very possible and you can have a great time. I suggest you hook up with some shanghai girls before leaving, perhaps via
www.match.com or
www.friendfinder.com. That way you'll find fantastic girls that you will give you a cool girlfriend experience and not ruin you financially.
Well, that's my 2 cents...
The hooker scene changes a lot due to police crackdowns, so you'll probably need updated info from the people who are there now, as previously mentioned.
I am considering going back in the near future, so hopefully they will write some good tips soon.
Good luck