Have you thought of a "wish list" in which users can link to any product found on the web that would like to receive as a gift?
I suppose it would be acceptable if you created a "wish list" in your own "About me" box (just don't expect to get anything from it), but to create a feature which allows users to create a wish list seems shady at best.
This would give you direct access to statistics on the consumption habits (divided by age, income, education, etc.)
In what way? The majority of users don't input their age, Stack Overflow has no idea about anyone's income or education unless they specifically state it in their "About me" box.
and would give you the opportunity to also contact the producers directly to inform them of these preferences
Why would Stack Exchange sites have any interest in doing that? Do you expect producers to pay for the information? Because producers aren't willing to pay to learn how many programmers on a website said they wanted one of their products. It would be, quite frankly, a pointless statistic because there's not enough variables defined and not enough people would fill out the wish list to make it worthwhile anyways.
encourage commercial activities targeted on the site.
Because that's exactly what we want. Maybe we could create some spam bots that let everyone know about the latest penis enlargement pill products while we're at it, too.