Wow, great thanks Sergio. I have not seen the quoted info.
I understand totally, we always try to look at it from the users point of view.
We do not use the date archives on the site, so having the content in date folders I cant see adding any benefit.
I think the site can do a great deal better with the rankings certainly, but it is on the way up 
We get a few interactions, but not many. Would like a lot more
Some of the URLs are getting very long also, so that another reason we would like to change the permalinks
I have also noticed that some of the older posts are dropping down the rankings. It appears a little faster then normal. This may not be anything to do with the permalinks, but its a thought i have had
It would be great if we could just somehow start all the posts from now onwards using the /%postname%/ structure. And all the past articles staying the same URL.
I dont see why we would have to change the already existing URL's of the past articles.
Is that possible do you know on a wordpress site?