I reviewed your website and here is my initial analysis and observations on what I would improve.  Overall you have a lot of good information and diversity of content (blog, video, podcast, reports, and tools) that’s outstanding.  Also you have a decent page rank (4) and a number of links pointing to your site.  The main improvement your site needs is proper optimization and link building (pages setup to target specific keywords and emphasis on building links to also target those same words.) 

Although I did check out your entire list of sites, I focused most of my review on your most established website (url removed for privacy/) and separated my review into three categories:  SEO (Search Engine Optimization) or things that would affect search engine rankings, design / aesthetics and usability, or how easy it is for users to find and accomplish tasks.

From an SEO standpoint

The website is missing key elements required for the search engines to understand what the page is about. Some of these are not visible to the end user (or person viewing your site), but are very important for ranking on the search engines. 

These are:

1. No header tags.
2. No keyword targeting on individual pages, each page needs to specifically target exact keyword phrases that a buyer/seller would type in.
3. The actual code uses a lot of JavaScript and code heavy ways of accomplishing functions that could be greatly reduced, decreasing load time and “text to code ratio”, which will help rankings.
4. Since you have a lot of different websites, it would be better to have them all integrated to promote one single site

From a design standpoint

1. All the sections look the same, I think the graphic design could be visually spiced up and the text itself could be laid out with some variation (headers, sub headers, block quotes, etc)

From a Usability standpoint

1. Navigation on the left hand side is very hard to scan because its small font and there are too many items under each subheading.  Changing it to 5 items per sub header and adding white space would make it a lot easier to read / scan.
2. Links go out to PDFs, different websites, and different looking pages without any warning or intuitive jump. 
3. Forms have many fields, but no option for a quick contact only field.

That’s a lot of info and I could have typed more, but although I can see a lot of potential improvements from a design and usability perspective I think your site would convert (get you business) if you got enough traffic to it. 

In order to rank on the search engine and bring targeted traffic to your site, you don’t need another blog or any other add-ons, just a solid SEO campaign.  If you wanted to address everything at once, you could rebuild around a more effective content management system, but that would cost a lot more.

At the very least I recommend.

1. A 3 month SEO campaign which would consist of optimizing all your existing content to target specific keywords and work on some link building to boost traffic levels and achieve search engine rankings.  Rankings can be achieved within 3 months (your site already has a limited presence, some links and is in a good starting position)

Then I would consider:

1.  A monthly SEO plan in order to maintain rankings and stay competitive.

Ideally or eventually

You may want to consolidate all your existing resources and websites into a newly designed SEO optimized site built from scratch on a content management system which would allow you to change all the pages / content yourself and optimize new pages / posts for specific keywords without needing a web designer.