Well, here's a link regarding the
Tritec plant in Brazil.
European car manufacturers (if memory serves) face or will face stiff tax penalties if their "fleet average" drops below a certain level of fuel economy. I seriously doubt that BMW is in a position to produce a small fuel efficient four-cylinder engine. Most of their effort is in getting power, not efficiency (which is not to say that BMW engines are wasteful, exactly, just that their design goals are biased towards high output).
Now, I don't know the business decision, but it seems to me that going in on a Brazilian factory would buy BMW some time if they wanted to design their own 4-cyl. They could also decide *not* to if the Tritec engine is smooth enough, powerful enough, and efficient enough -- after all, the BMW brand is still safe. Real BMWs still will get real BMW engines.
Oh, and don't discount thermoplastics. Plastic has come a long way. I think a cam cover is a good place for plastic, and if it frees up funds to produce better piston rings or other essential parts (Dana Corp. is producing the cam cover, rings, and seals) then the plastic's a good thing. Plastic's light, too.