So far I've always got a full pass for the congresses I've attended, and I did learn a lot of things from workshops. For example, I learned to dance on2 from congress workshops, and also afrocuban rumba. I've also taken some very good body movement and styling workshops (these classes are not available locally). I even learned things from partner work classes as a follower, thanks to some excellent teachers. At the NY congress, however, I didn't take many workshops (mainly because of the time I had to spend for the survival challenge), and in hindsight a party pass would have been enough. If the workshop schedule is already out, you can check and decide if you find enough workshops that look interesting. If not, check the teacher listing and see how many teachers you want to take classes with. If the listing doesn't look particularly attractive, then go for a party pass (plus a private lesson or two perhaps).
Sag, I'm sure I saw a party pass option for the NY congress - maybe the organisers added it later?