Porsche will need several years and more than a billion dollars to compete in F1. The first few seasons will be a disaster for Porsche and hugely embarressing (that's the nature of intense F1 competition). Ferrari is being slaughtered by Renault this season, and Porsche will ruin their brand if they compete.

I'd rather see Porsche spend the money on improving the 911, but F1 is a sunk cost that will never payoff.

Don't forget that the Porsche brand aura is largely perception. They are not invincible anymore as competition has cought-up (and sometimes gone ahead).

A single F1 season will destroy the Porsche brand.