i think from a business standpoint, there's not much money to be made in a racing circuit. consider first the cost of the land, if ever you're gonna buy it. you're gonna need big space, maybe 5 hectares. so that means it has to be in a province. then the cost of constructing an FIA-grade circuit itself, plus hospitality suites, plus proper garages, would certainly be astronomical.
now how can you make money out of it? the best way would be advertising. how do you attract companies to advertise in the circuit? best way is to have TV coverage in all the racing series being held at your circuit. here now lies the problem, do we have a local racing series right now that has a contract for TV coverage? no. you're gonna have to host a regional motorsport event like GP2 asia, AFOS, asian touring cars and the like. i'm not sure, but you're still going to have to pay for hosting license, if ever they consider the venue. when hosting international motorsports, you're area should be prepared for the influx of foreign people coming in. so facilities such as hotels, restaurants should be present.
another way to recoup your expense would be some form of subsidy from the local government, since you could argue that you are boosting local economy by attracting visitors to the area. holding track days will also net you some money, but i imagine this will be small amount. rely on it solely, then you grow old and still not get ROI. an example of corporate events brent mentioned are the porsche driving clinic, or BMW media tests. i don't know how much they pay but surely more than track days.
it's a vicious cycle this business is. personally i wouldn't recommend it. if you're going to depend your daily life on it. don't. but if you already have an existing business and you're bleeding money from every orifice, then as a die-hard motorsport fan, DO IT!