Hi Niceman
From past experience this may be only a temporary decrease is position.
Before i did a website revamp on a site i used to own (kiddiekids-co-uk) it was always sitting on page 2 of google for the search term "baby names". When i updated the page with new content and design i noticed the page fell to the middle of page 3 for the same search term. After 2 or 3 weeks it had moved back upto the top of page 2 with the odd position on the bottom of page 1.
It now shows around the middle of page one for that search term.
My advice would be to give it a little bit of time to stabalize in the search engine positions for the new content.
Lee