Well, the idea of marrying Philip was not a stupid one. Of course Elizabeth would have never went through a Catholic conversion but Philip's lack of OFFICIAL control of England's affairs had been proved during his marriage to Mary, in which he signed a contract not to interfere in politics, although he did it.
At first Philip didn't have wanted to marry Mary and asked her father to marry the Queen himself, but Charles refused. It was then when Philip developped an ambition towards the English Crown.
Elizabeth, years later, would be near to marrying another Royal, Prince Hercule François de Valois, Duke of Alençon and brother of King Henry III of France. He was 22 years younger than she was and the marriage didn't take place in the end.