Structural SEO problem on PubBB : solutions ?

Hello,

After an analysis of Google bot fetching, on Google webmaster tools, I've understood that structuration of topic pages are very NOT SEO at all : indeed, we have the keyword "post", "forum", "registered", member", "guest", "reply" as "most common keywords". First bad point.

Secondly, if you watch how pages are seen by Googlebots, you understand that titles H2 are used for words "post, and H3 for the name of posters, instead of forusing on the content, the code is "code oriented", and not "content oriented"

H1 (title) is OK, and titles of topics are well referenced, but content of discussions is very badly SEO structured, the content is not SEO highlighted. It is quite normal as PunBB have been developed slightly before the huge success of Google. But todey, it is a problem.

Last thing, URL rewriting has recently been made on my website (with 301 redirection and (regular) resubmitting of sitemap), and the results are quite horrific : PR getting down, well ranked pages in google getting down, new visitors daily diminishing.

Does anyone has an idea of how counter-thwarting this ?