(un)fortunately they're closely related for most people; the more sex you have, the better you get at it.
Yes, but I was thinking more about standards (your partners' skills, looks, passion etc.), not frequency.
Now, having a stable partner has its benefits (such as learning exactly what the other person likes, experimenting more, etc.) but I've almost never said no to a one night stand. But I'm a person of lax morals, so YMMV.
Stable "access" to someone you really like is an important benefit to me.
I usually don't connect morals and one night stands per se. :)