Some common sense
F1 attract tourist -> Tourist spend money -> Shops earn money from tourist -> Bosses(Elites) make profit -> Guess who earns a salary from working in those shop and get a higher bonus due to increase revenue?
Unless we only have vending machines and automate everything else, the F1 helps bring in the tourist money and it helps create jobs. Just to name a few of those who benefit from F1 - Restaurant, Night Spots, Hotels, Retail Shops, Tour Agencies, Airlines, Event Organizers, contractors in charge of setting up the venues, Public transports, Cab company, "Integrated Resorts", etc.
1)require more man power -> 2)Create more jobs -> 3)Due to increase in number of tourist -> 4)Spending more money which brings in more revenue -> 5)Extra media exposure of SG to the rest of the world -> 6)Which will make more tourist want to come here -> Go back to point 1)
The benefits of does not just benefit the country/pple during the event itself. There is a lot of intangible benefits that get associated with such events. Throughout my travels, I know of many pple who have never even heard of SG let alone seen it, the media exposure given by this type of events help bring in more tourist money