Good question, larc.
When religion is a factor,(aside from just finding someone they think they can't live without, period) I think that JW men choose worldly women primarily for the first two reasons you site, and in that order.
A lot of the sisters would fool around but there is that danger that her conscience will kick in and buddy when she starts blabbing, your goose is cooked. There is also the factor of having to face this little dish at all the meetings as well. Will her eyes give her away? Will yours? Suppose you're in the same car group with her out in service? How will you keep your face from getting red when you're doing your #4 talk on the evils of fornication? What about your comments at the WT study? You would definitely have to be careful there too. And then there's that annoying fact that you know, she knows you're a hypocrite. And the awful fear that somehow she might one day bring it up during one of your romantic interludes and force you to see yourself for what you are. She might say something like this: "It's too bad that you and I will never be in the paradise earth, isn't it?"--a real downer in an otherwise uplifting situation if you get my drift. A worldly gal would never bring up something like that. She would do her thing, pick up her crucifix necklace off the motel nite stand, and go to her church on Sunday and think nothing of it.
Then there's number two: Forbidden fruit is always the sweetest. Ask anyone who's ever stolen a watermelon if you don't believe me! This is especially a factor when the guy definitely does not want a permanent relationship which brings us to another, closely related point. The guy knows (at least he thinks he knows!) that he cannot marry this woman so it enables him to set up his emotional shields to keep this fling from becoming something meaningful.