Something I only realized after I did it was that a few of my old posts are absolutely choked with spam, as in, hundreds or possibly thousands of garbage porn-spam comments on one post (I had anonymous comments enabled but screened). One thing Dreamwidth doesn't have that LJ eventually did get around to adding is a "nuke all screened/suspicious comments" button, so it probably would have been better for me to notice that before the import.

At any event, I bit the bullet and restricted commenting to registered accounts on Dreamwidth.