@luf: Just in case... wanted to give a small update that i fixed the issues regarding contacts missing when phonebook accessed from carkit. Also, file transfer issues are solved. (Un-)Fortuately, that meant switching phone model and OS (now running on Android).
I'm sorry, but from now on that also means i'm not available for analyzing things/tests for bluez and PBAP etc., as the N900 is now delegated to "spare gadget"/2nd SIM for travel usage. Just finally too tired to have so many half-supported and non-working but time-consuming things under Maemo.
Thank you very much for all your efforts!