I think it might be copyright problematic to share proprietary presets.
Probably not as much in spirit (because the presets would presumably be useless without the plugin), but more by strict copyright law.
For example the hypothetical case of a cracked version of a plugin not having presets could create the awkward problem of shared factory presets actually making a difference.
Sharing utility scripts and programs to perform one’s own conversion would probably copyright safer. That would be more analogous to ripping a CD I purchased legally, so I can play it in my iPod (to use an old school analogy).