The best approach for a case note is to outline the main issue before the court. Then very briefly the material facts. The next stage is to outline the key steps in the court's reasoning as they arrived at their decision. The most important part is then to examine the legal significance of the case and for 70 or above the social and economic impact of the case.
I suppose it depends on the criteria being applied. However, at Level 2 and 3 most Law Schools ask for an awareness of the practical implication of the law/a judgment. Example: if a case is set on broadening the rules of consideration in contract law to uphold more agreements to accept less = issue with use of economic duress to procure such agreements = in the post credit crunch era a likelihood of more consumers being allowed to wipe off more debts = impact on business. I also came across a wonderful case analysis recently where the student was able to show how a case would impact on the financial markets. It is original ideas like that with a social or economic angle that can boost marks. However, I take your point - legal impact is key.
I definitely agree, but I think that lends itself more naturally to some cases than others. In most cases I find attempting to discuss 'societal impact' tends to lead down the road of policy issues etc, which can be pretty fluffy at times.