There most definately can be a happy ending. I've got several friends who met and married spa women. Even been to one of their weddings. And I've had a couple of relationships with spa girls, as well. And not just happy ending girls, but FS girls. One thing that is difficult though is the language barrier. After you've had sex you have to talk and share feelings. And that can be tough when you're using google translate.
Another thing is getting past the fact that she has had sex with hundreds of guys (of course, you've had sex with hundreds of girls, but that doesn't matter, right?). Sex for money is different than sex in a relationship and the fact that she has done (wild) things to other men for money can be a turnoff.
I've not found any girl to be money-hungry. Just willing to have a relationship. Although they can be naive about what a relationship really is all about, American style.
Lastly, they don't have uppermiddle class wanna be white girl attitude. Although I suppose in one more generation the asians will catch on to that American style.