Microsite question

A long time ago my boss brought a lot of domains related to the recipe vertical (this is an online publisher that has among other things a recipe site). These are very specific urls (for example one is about Fourth of July recipes and another is about buffalo chicken wings). They at one time housed microsites and now have nothing.

Presently, they redirect to the main recipe site. The July Fourth page goes to a listing on the main recipe page that talks about Fourth of July recipes.

Now the question is what to do with these url's? Is it better to leave them as redirects (I am assuming that they are 301's, but will have to ask), ditch them or use them as microsites, each with relevant content with a link to the main recipe page (but not to each other, of course).

Would the microsites be considered gateway pages? If the link says something along the lines of "Like this recipe? Find thousands more like it at..." would that text alone make it a gateway page? Another option would be to have along with the recipe a place to sign up for the main sites newsletter (a big part of the business model here is getting people to subscribe to our various newsletters). The link in this case would just be a basic link to the site without any of the previous text.