2- through my experience of teaching i have noticed that if we want to make the lesson interesting for the students , the best way is to make the lesson more personalised , students like to talk about their activities and they like to talk about themselves , and specially if they do the activity in pairs and they can choose their partner , this way you will notice more controlled and useful activity, so as a conclusion , engaging the students more personally in an activity will give better results
4- teaching a receptive grammar activities can be useful for people who are looking for learning the language and not looking for an academic degree which means they know enough language to deliver the meaning and it is not about the form.
as for students studying productive grammar activities i will say they are more involved in academics and they need a very neat and organised way of speaking and writing like writers and people who work in schools and universities.