A couple more advantages of WordPress:
- Ease of installation. I know I found the prospect of installing MT very daunting, but with WordPress you just need to upload everything, chmod one file (optional) and run the install script.
- Fewer templates to configure. You have index.php and your comments page, and that's basically it. Most of the minor aspects of your blog's appearance (like how archives are displayed) are controlled through parameters in your template tags.
- Ability to password-protect individual posts. I don't use this myself, but I know people who've installed an MT hack to do the same thing.
That said, I'd expand on your first two stated advantages of MT: basically it's been around for longer so the knowledge base is larger. WP documentation is still very rough around the edges compared to MT, though we have a dedicated team of users at work on it.
And, in response to your specific queries: WordPress has tags for previous and next entries, though I don't know whether your current numbered page setup would be achievable. According to the wiki, post counts per category can be displayed in the sidebar. Showing an extract from the post ought be possible, since there's an 'extract' field which can be configured to default to the first [x] words in a post, but I'm still trying to figure out how to call it. You'd probably need a hack to do the same thing for comments.
Hope that helps :)