[T2DMan]

Are we talking about two different things? A vbseo Google sitemap, and vbseo rewrites.

A Google sitemap certainly helps Google to find your threads, and so can decrease your server load, as you are directing Google to visit specific pages more or less often. The sitemap is generated as often as you request it - either by cron, scheduled tasks or manually. There is only server load created at that instant.

(Once we update to vb 3.5, google has become more friendly) - yes, vb3.5 included many seo orientated changes, a lot of which were at my instigation. But vbulletin didnt finish the job. vbseo rewrites plus some onpage optimization, plus getting suffucient links - gives what I consider a completed seo of a forum.

Is it going to increase server load? -vbseo rewrites does increase server load, and on some servers and large forums this has been an issue. But with large forums some rewrites can be turned off, and tweaks made to get load to acceptable levels.

Estimatedly, how many pages would this help to be cached daily? - never any gaurantees about anything. But when you have clean url's, no duplicates, etc at least Google/yahoo are given the opportunity to find url's easier.

After this, are robots just going to visit the site maps? Google uses the sitemaps as a url list to then visit the actual url's. It also spiders url's that are not on the sitemaps, url's that it finds via normal spidering around the web.

Is it going to help earnng outbound links? - if your pages are able to be found on Google/Yahoo, then you are more likely to get people linking to you. So sitemaps will help pages get cached faster, and if they are seo'ed well etc then they should rank well...