Specialised conversion/migration software is probably the better route to go, especially now that the Eudora source code was donated to the Computer History Museum. I'll give Eudora2Unix a shot though!
You mentioned attachment name clashes: Eudora simply appends an incrementing integer to the incoming attachment's filename, for example, it would retain file.jpg for the first email and use file1.jpg in the next email it encounters.
Note that its "pine" output format is... almost what Thunderbird wants, except for nested mailbox effects. That'll require renaming directories from foo to foo.sbd and sometimes adding a corresponding blank foo file.