Hi,
Adding an active blog, one that receives interaction (real comments, links, etc) will certainly help your new site in a number of ways.
Make sure you create URL's on the new site that match your old blog.
For example
www.oldblog.com/newworldpinotnoirvsoldworld.
Should 301 redirect to
newsite.com/blog/newworldpinotnoirvsoldworld.
and not to the new sites blog homepage.
This will replace rankings for the old site with the new one. It will also introduce your current blog audience to your new site, among other things.
I would recommend warning readers that the change is going to take place at least a few weeks before so you don't put people off when they are suddenly redirected to a new site. On site notes or even an email would be nice.
Hope that helps.
Kyle.