Now BMW has the new generation of 3 series, they should re-entry to WTCC with factory team for marketing purpose!
IMO, BMW should focus on the following races with their official team:
WTCC – the most exciting race, a lot of overtaking, the racecars are close to the street car so got most recognition from the mass audiences.
GT Class (ALMS, VLN, 24 hours Nürburgring, Le Mans) – also very exciting race, cool looking cars and the competition among Ferrari, and Corvette will bring up its brand image.
DTM – super cool looking car for marketing purpose! The race itself is boring. Hopefully the introduction of DRS and option tyres will bring in more actions and overtaking maneuvers this year.
It is wise that BMW stays away from F1 race, too expensive for the game but may be they can provide engine to some F1 teams in order to keep BMW associate with F1 for marketing purpose.