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If it has inbound links, I would 301, assuming the topic is at least the same. If it has no inbound links, I would probably delete it and allow the page to 404. It seems webmasters keep creating new pages on the same topic, rather than improving the content on the older page. It doesn't make sense.

Gotta disagree with this one.  Creating high quality blog content with the same keywords you are targeting on your products page can be a good strategy.  The blog post will add more content related to your keyword on your site, increasing relevancy.  It's also a lot easier to build links to a blog than a product page. Just make sure to link from the blog post to the product page, and the product page can get a boost.  If you rank really high in Google, you could even get 2 listings for that keyword.  If for some reason the blog content outranks the product page, you can just take that same content and throw it on the product page with a canonical from the blog post.  If all else fails, you can 301 redirect it.