Iran spent heavily on modernization, industrialization, and education programs from the 1960s until the 1979 Revolution. It was able to achieve a lot relatively quickly, putting in place infrastructure, industry, and a scientific base that continues to benefit the country today. However, some argue that this rapid modernization helped kick off the Revolution, as it threatened traditional authorities but failed to move quickly enough to result in jobs for the increasing number of trained and educated Iranians who would have formed a content or pro-Shah middle class. Imperial Iran also spent a massive amount of money on military equipment and training (there's a list
here).
Saudi Arabia could have pursued a program at least as ambitious as the one planned by the Shah, and have had money left over too. Saudi Arabia had twice as much petroleum production as Imperial Iran (around ten million barrels per day) and a population of around 6.5 million. With petroleum selling for around $22.50 (inflation adjusted, from
here) per barrel throughout the 1960s and 1970s prior to the 1973 Energy Crisis, the Saudis would have been bringing in the equivalent of $225 million per day, or $82.13 billion per year.
So, what might have happened if Saudi Arabia had spent at least proportionately as much on modernization and its military as Imperial Iran had? Could it have developed a relatively diversified economy like Iran? Would stability have been an issue? Could it have acquired advanced military and nuclear technology on par with that acquired by Imperial Iran?