Yes only attend if your W is working on the marriage. How do you know? She reads the 5 Love Languages and learns yours and actively try’s to implement them. She does the homework given. She speaks positively about you in MC.
Anything less is a complete waste of money and time but of course MC is not going to tell you that.
So that basically means (if I'm hearing you correctly) that any couple that is currently S should not do MC, right? My WAW certainly knows my love language and to her credit, speaks positively about me but since we're S, we don't have much of a pathway to implementing them.