A 5 year old site with roughly 5,000 pages had a new feature added 30 days ago, a dynamic classifieds section, and the number of indexed pages climbed to 50,000 quickly.
Webmaster tools shows only 7000 pages have an internal link to the home page thus far so it is playing catchup still.
The pages, being classifieds, will expire in 6 months and return no content while new pages are added daily. A 410 gone page with links to the main classified categories is in place to redirect traffic while managing search crawlers.
The pages have original images, titles and text that is specific to the classified item type (100's of types) as well as description snippets (these are also made available to other sites). Search seems to find them appealing so they aren't being considered too similar.
Concerns: Eventually there will be roughly 70,000 pages of constantly expiring classifieds. The search value of these classifieds is of no importance to the owner one way or another but the search importance of the original 5,000 pages is extreme (for business reasons). Care was taken not to destroy the existing internal distribution of PR. Do the classifieds pose a threat, as described, to the ranking of the sites original pages simply because of sheer volume? Is there anything else you'd do or change to protect the rankings of the original pages?
note: robots.txt block of classifieds was considered but because adding new pages without benefiting from the return pr flow to index it was not ideal it wasn't used. Competing sites don't block theirs either.
Any opinions welcome.
