reginos:

I think that McLaren Automotive would have been more useful to BMW than VAG.

In the case of the VW Group McLaren's added value will be small given that Porsche and Lamborghini cover VAG very well.

McLaren Formula 1 Team  is different. BMW have been in and out of F1 racing and surely they wouldn't want to be involved again. OTOH the VW Group would like to try F1, Porsche wish to supply engines and thus McLaren offers a ready solution to both.

The prospect of a Porsche powered McLaren F1 car excites me as it brings back memories of those golden years almost 40 years ago with my favourite team, engine supplier and drivers winning 3 drivers' and 2 constructors' titles.

 

 

I think this is the core of the challenge, the McLaren car business fits best with BMW and the F1 team is of most interest to VAG.  However you cant really separate the two.