Old content makes your site look neglected. If you neglect your site what do you do to your clients? People will stay away. Keep your content fresh and up to date. Be sure that prices are correct and offers are relevant. Keep changing images of products and services. Post new testimonials too to keep things moving.
As to the blog: if you have a blog then you must commit to it. That means AT LEAST one post a week; if not two. They don’t have to be long but they do need to be frequent. If this is too much commitment then DO NOT HAVE A BLOG!
Far better to have a news or article page that you can update as and when you have something to say and the time to write it down.
The reason for having a blog is to share news and relevant content regularly. If you can’t commit don’t do it!
The reason that I wrote this post is because I noticed that I had not posted on this blog for over a month! Horror; I am too busy posting on other blogs to keep up on my own; shame on me, and I must do better! ...watch this space!