I totally agree, no need to shoot for 51% to control a company, with 20% Porsche will get a significant influence over VW.

Their track record is impressive enough to make sure VW's management will listen to their advices.

VW is just in the middle of a massive cost cutting plan that should yield to a very strong recovery in margin terms ...

Porsche will benefit from cost sharing, share price appreciation (which is highly likely over the next decade for example) and the dividend stream... The bottom line they believe they will get at least 15% return on their investment ( Euro 3.5bn) over the medium term.

I wouldn't buy the 2 shares, I would just buy Porsche because I get exposure to both companies in one shot.