Yes, you are right, the word gigolo is outdated and it went out with the popularity of H.James, yet this fortune-hunting behaviour remains prevalent among social alpinists (including wisteria sisters - with only one prize slipping the hook) that married into the BRF. So what Prince Philip was intelligent - do you think there were no intelligent and SOLVENT royal princes in Europe for HM to marry? Her equals, I mean, not penniless refugees (like Prince Philip) who would never forgive her higher status and would forever punish her with affairs? As for the Italian gigolo - I don't even have the right word for him - what do you call a man who abandons his 'partner' and their young child and runs after a royal princess to better his status?
You are right, nobody owns a crystal ball and can predict the future, but surely one of the most basic rules is to marry your equal (intellectually, financially, socially, religiously) to avoid the inevitable thoughts of 'ah, she/he married up/down, for money/status/whatever'. Unequal alliances never end well, even if they are tolerated for decades - why do you think Prince Philip's will will be kept top secret for 100 years to protect the dignity of the Queen (official wording)?