RJM,
here you are wrong. Even if you export via MPL file, you cannot import user defined fields via MPL file. The fields have to be defined beforehand in the library, otherwise user defined fields will not be imported. In an MPL file you only have the information about the field name, but not any other information about other field attributes. The import does not know whether you are going to import a standard field or a list field.
I have found two workarounds. They work but are not very satisfying as a dump of all database fields which every SQL database incorporates.
1. Create a new library from your existing library by cloning the existing library in Library Manager, then clear the whole library content. You will have an empty library with all the existing fields.
Disadvantage: The library is not really empty, As information is only unlinked, but not deleted. The library files still contain all the deleted information. If you want to create a fresh, empty library for somebody else, this might not be a good solution.
2. Create a new library from scratch with all the needed user defined fields and view schemes and name it ie. "MyDefault Lib" and keep it empty. Whenever you need to create a new library of the same type, proceed as above, but clone the new library from the empty, personal default library. Then you really have a fresh new empty library.
Disadvantage: Whenever you make field or view scheme (and probably also playlists) changes in your main library, you have to make the same changes in your personal default library, Can become very annoying as times goes on, as you always have to keep track of changes.
MC12 fundamentally lacks a tool to dump the data base design (including field definitions*, view schemes, playlists etc.) to a file (could be an xml file), so that this file can be used to create a new database with another name. Such a tool is included in all mayor SQL databases.
This this is a long standing feature request for the future.
*) this includes also the standard fields and standard view schemes as some attributes like the display name can also be modified.