If you have your own server, just download a free PHP sitemap generator from Github and set up a chron job to run it whenever and however you want. I just did that and no longer have to worry about XenForo's built-in sitemap tool.
I am now submitting to Google just the index page, nodes, and threads. The rest Google can find on its own, if it feels like it. I'd rather have fewer good pages indexed than lots of crappy ones.