Blogs build relationships. Dealers become part of their local community by sponsoring events, charity, etc. This is an extension of that at a lower cost, but I would say a mix of all is best until you know what the readers really want.

I think it depends on the audience though, and what starts to build the discussion on the site. If more readers start to respond to products vs. events or happenings at the dealer then it might be better to stick to products until the audience gets more invested in what is happening at the dealer.