I just set up a dev.domain.com subdomain and mirror everything there, doing a find/replace on the sql export for www > dev, and of course changing wp-config.
I used to have a staging server I mirrored things on, but I’ve since learned that a change in length of the domain name will invalidate any serialized data that contains it, so I now always keep the staging domain the same length as the live domain.
You could also not sync the comments table so you don’t overwrite interim comments, as long as post IDs don’t change I don’t think this should be an issue.