I asked someone with greater plugin development experience than mine to look into it and it looks like the standard import/export doesn’t provide the necessary hooks for an easy solution. Added to which, if your custom menu includes things like links to your blog’s Pages, how do you export those without referencing specific page ids etc?
I can see how this would be useful if you were creating custom menus that contained nothing but external links…but internal links…?
It’s for transfering between blogs with a similar set of pages, so was hoping that the permalink structure would allow the menus to continue to work. But in a wider sense I can see why that is the reason why the export / import of menu definitions doesn’t exist. Poot. Will have to look into the database (Or just recreate the menus. 😉