In a similar vein, I'd love to ditch iTunes too now that it's more of an iTunes Store portal than a library manager, but I rely on certain metadata that I don't think are included in the tags, things like date added and date modified.
[Date Modified] is tracked by the filesystem, and should be preserved properly no matter what.
[Date Added] is specific to the database (it is, literally, the date it was added to iTunes), and therefore would be different. MC has its own "Date Added" field, called [Date Imported]. You could, conceivably migrate this data over, but it might not be easy as iTunes doesn't have the most robust metadata export functionality.
Someone who knows how iTunes handles in-file tagging would have to comment on whether the iTunes-specific Data Added field is actually included in the file tags (which would be the easiest way to migrate it over).
PS. It looks like from
the briefest of Google searches that it is possible to export the data from iTunes and get it into an Excel-capable text file of some kind. From there, you should be able to import the data into MC with relative ease, if you import the files "in-place".
There might be other ways too... I haven't used iTunes seriously in so long that I haven't followed this very closely. MC can import Playlists, including XML type lists, so it is possible that just exporting the entire iTunes database to an XML, and then importing that XML into MC would handle this automatically.