I imported one of my Tumblr blogs using WordPress’ Tumblr importer. Re-Reading Les Mis started out as just a mirror of the corresponding blog, but I did the occasional image post or repost-with-commentary, and after finishing the original series covering the entire book, I started posting excerpts & follow-up commentary, some of which made it back to the source.
I’ve updated my What’s in your archive? post. The importer does a good job of transferring your blog directly from Tumblr to a WordPress blog. It even imports images (though sometimes it imports a single-image post as a gallery for some reason). The original URL is stored in a custom field, and you can leave it connected and import new items when you want to bring them in.
Some gotchas: It can only map to one author, but you get to choose which one. It puts everything in the default category. Videos don’t get imported, even if you’ve just embedded a YouTube video.
There are only ~150 posts in the Les Mis Tumblr, and not much overlap with other material (though again, a lot of the early stuff is just mirroring). There are closer to 1500 1700 on my main Tumblr, and the vast majority of it is automatic shares from K2R, Instagram, or Flickr.