I also wish it was possible to more easily display lengthy comments. The tab idea here seems like the best way.
I've tried playing with variations of the suggestions in this post
http://getmusicbee.com/forum/index.php?topic=3006.0 but they are not too satisfying for comment viewing. There is plenty of room for more tabs besides "Artwork", "Details", and "Lyrics" in the "Now Playing" area.
As an alternative, another place where comments could be visible is in the "playing track layout" area. In addition to web sources, maybe there could be a way to display track tags here?
Just thoughts... MusicBee is awesome even without this type of function.