Instead of using margin and volume to make your web analytics framework, It may be easier to build it out using a conversion funnel. The different steps of the funnel give you ideas and starting points for brainstorming the functions your site has. It also forces you to think through your marketing and web analytics strategy for each step of the customer acquisition cycle. The steps are awareness, consideration (desire, interest), conversion, loyalty and advocacy.
Each step has Key Performance Indicators and their associated targets and goal values. For some of the goal values you’ll have to determine internally, (Avinash’s post on this is rad) and other goal values are the Per Visit Values calculated by Google Analytics (dividing revenue by visits).

I like this kind of view because it puts into prospective where the majority of your advertising efforts are going. It’s easy to heavy up on everything leading up to the conversion and then forget about loyalty and advocacy, or vice-versa.