(2) those aspects of my dancing that prompt such a question are often not at all things that I learned or picked up in a salsa class
Beginners what to know "when will I get good". But when they get an answer what do they process out of it?
Some people have the rhythm straight away :99% of the women/1% of the men
Some have either dance experience or attributes from sports/martial arts such
as co-ordination, balance, fitness and knowing how to reference moves so they remember them easily. This is why there is a varied level even in a beginners class.
The thing is though I see beginners in awe seeing basic movements for the first time. They may also stay behind and watch the intermediate or advanced class wondering when they can do these things. If they think it takes many years to do a few moves they will run. If they can have an accessment like "when you complete the beginners course most people can do this" at least it's as honest as possible.
When they're hooked you can give them the bad news that to get really good it's takes a lot of work