I'd much prefer the xmlhttprequest type ajax calls than a "read more..." link.
You just feed the call back to a page that returns the rest of the content from the database. (Or flatfile if you prefer it really doesn't matter how it's stored)
If you're already generating the SEO pages and dumping them when the item is updated they can still be linked from the main article and made available to other sites etc..., but for people viewing the site from just the main page I'd think it's much better to have all the data available without a whole page load.
(This would actually be better for the server also, but it will cut down on advertising impressions.)
Lastly just wanted to add that ajax although it's been abuzz for a while now is really just a javascript include file and some DIV tags for an innerHtml write, tied together with a simple dynamic page serverside that generates the extra information.
There's a great tutorial that covers the basics here.
http://www.w3schools.com/ajax/default.asp