If I increase my site size from about 100 pages to over 100,000, I expect that should really increase my weight. Is this correct, and do I need to do anything to get the server to re-evaluate my weight?
There is sporatic checking or validation of your site and/or you can manually validate your site if you have a Google API key. Anytime a validation happens your weight can change if you increase the number of google indexed pages, pr changes or whatever other factors the coop takes. I think the first two are the most important.
Login to your account. Edit Account Settings. Input your API Key. Hit Submit. Then click on Validate/Calculate Weight Now.
Also ... the new pages would have to get into the google index before they contributed towards your weight.