Yes, less is more should definitely be the message and is one we stress again and again on our Luke-less Delta course here in Buenos Aires.
Another extension to your dialogue ideas is the ‘half a dialogue’, which can be used as revision of a certain dialogue or as a way into a new one. The idea is that if you have a dialogue between A and B (hopefully written by the students) one group gets the A lines and the other the B lines. What they have to do is write the other speaker’s lines of the dialogue (As write B lines and vice versa) on a separate piece of paper, leaving lines free between the lines they write. Then the groups swap papers and have to complete the half dialogues written by the other group, creating a new dialogue completely written by the class. this can then be compared to the original dialogue and any interesting differences (i.e. students using simpler language than the original) can be noted, or they can just be mined, mined, mined in their own right.