Halfdeck - 6:36 am on Jun 19, 2006 (gmt 0)

1. Sitemaps help Google find pages it didn't already know about. As far as I know, it doesn't cause pages to turn supplemental.

2. Absolute paths - irrelevant I think.

3. "I changed my parameter from?Id=346 to?property=346"

It sounds like your site is DB-driven, which often means thin on content, identical/similar META descriptions, and various urls pulling up the same page.

Do you have meaty paragraphs on every page? How many words do you have per page NOT including anchor text and stop words?