lucy24 - 9:44 pm on Jun 12, 2013 (gmt 0)
It depends on how many pages your average visitor hits. My initial reaction was the same: 250 lines is nothing. Then I took a quick look at my own sharedstyles.css (used by almost all pages in addition to directory-specific stylesheets). It's pretty exactly half that length, weighing in at 4.6k. That's already bigger than some of the pages it belongs to, before even throwing in the directory stylesheet which tends to be bigger. So it's worth it if your visitors hit multiple pages-- but if they tend to be in-and-out, one page, bounce, question answered on the first hit, you might be better off with in-page styles.
On the other hand-- back to your original question-- you'd want to keep some unused styles just in case you want to use them later. For example, I don't think I currently have a single <h6> anywhere on my entire site, but I'm not about to delete it from the CSS!