joined:Nov 28, 2002
Since then my traffic overall on the site has gone down
It's hard to say what's going on without knowing what portion of your traffic went down.
Was it the traffic to these particular pages, from these particular keywords that went down? What about the rankings for those keywords?
Or was it traffic that was going to other pages (probably pages that were on your main nav before) that were already doing well that went down? How are those pages ranking?
I would spend some time looking at the traffic for particular keywords and classes of keywords and try to find out exactly where the traffic loss is coming from, and then adjust your link structure to redirect juice accordingly.
As for how to boost these particular pages - make sure they're well-optimized (standard stuff, exact keyword match in title, body text, headings, image alt text etc) which it sounds like you've done, and then as Robert said, link to those pages with keyword-rich text from within the content of other closely related pages. That way you're not redistributing a lot of juice from your global nav, but you are increasing the relevance of those pages with on-topic links.
Another thing you might consider is optimizing another page for the same keyword, to try to get a second listing. That can increase your clickthrough a lot even if your ranking stays the same.