Know-How Exchange : Research/Metrics

I work in a technology firm that is looking into implementing a blog on our web site. While I have read all of the materials on blogging, both at marketingprofs.com and elsewhere, I'm still puzzled at how to measure the success (or lack thereof) of the blog project.

I need to justify the costs of implementing and maintaining a blog to management, but can't come up with better metrics other than the old standards:
~ Traffic stats (increased referrals to search engines, unique visitors to the site, etc.)
~ Inquiries from the blogging pages (measured via source coded inquiry forms, etc.)
~ Improvement on SEO rankings

Any thoughts/ideas on what measurements would show that a blog is successful?