Is there anything a student could or should do about a professor who gives lectures so dry that less than 10% of the class turn up?
That you asked the question shows that you feel that there is something that you can do, and that you somehow should do something. However, the question lacks motivation. The lecture is boring - OK. Many things in life are boring. Here are some different motivations you may have (certainly not an exhaustive list):


You would like to have better lecture for yourself to facilitate your learning. That's a good motivation. Especially, you can bring this point across without judging the lecturer or the lecture. Focus on what you experience and what you perceive. Note the difference of "I can not focus for the whole lecture." and "The lecture is boring." 
You feel with the students not coming, think they skip the lecture because they find it boring, and wish they would have better opportunities for learning. Note that students skip lectures for all kinds of reasons. I myself skipped lectures because I did not like the lecturer (although the lectures were anything else but boring), because the lecture were indeed boring, because I did not like the lecture style (e.g. it being to fast and reading from a book suited me better), because I was just "not in the mood" (although anything else was OK with the lecture). But it seem that you checked the premise. Then here be sure to stick to the facts when formulating your suggestions/feedback. Note the difference between "The students find your lecture boring." and "Other students I talked to agreed with me."
You want to help the poor lecturer. Also a valid motivation, but quite tough to deduce some action here. First, it's hard to be sure if the lecturer really wants help or could do something. 


So, there is no general advice in this situation. Some points to consider: Do not judge persons, do not blame anybody. Describe your experiences, suggest changes that would help you. Be prepared that nothing will happen and do not insist. Think twice before involving a third person.