After posting new content on your site, it is not taboo to go back and edit it later. Most visitors that come to the site are new, they do not know anything about you, so when they land on your site this is the first thing they see. If the first thing is an older post with some outdated information, they may not have a first good impression.
Overall, the site needs to be maintained an curated. As you learn new techniques in writing or find ways to add new value, you can apply that older blog posts. if you had a HowTo: on the proper way to install WordPress on your Mac, this could change depending on various factors. It is okay to go back and update the posts to reflect current trends and technologies.
This weekend, I plan to reboot my Christian-Gaming.com site that needs to be completely retooled from scratch. After a years of working with it, it has gotten super bloated with tons of images, tags and categories. Also, we want to revise the reviews for grammar, spelling and add additional ratings to help visitors make better decisions. This is the awesome thing about getting constructive feedback, it helps refocus your mission to provide more value.
If your blog post is written to reflect a moment in time, such as your 2013 goals, there is no need to update that. Much like my “Random” category, as a whole, I do not expect to back through and update these old posts. These are thoughts that I had at the time and I intend to leave them in a state that I can look back and reflect some day.
Your website can be a living, breathing entity. Improvements can be made to increase value to new visitors that visit your site for the first time.
Image Credit: UK Ministry of Defense