It's not about the engine really. It's all about having the capability and resources to build the engine that is balanced and will not destroy the vehicle it sits in. Any one with the resources can build thousand horsepower engines but not everyone can balance it and make it drivable. In essence, UR is showcasing their capability and technical know-how and putting it to the test. That's good for their business.
For the driver's (owner) stand point, it's all about having a machine that only a very, very few can own. Such drivers do use that power anyway by joining racing events. Believe me that if Pajero/Montero owners, Civic owners, Jiffy owners were racing, they'd up their engine's power and will use it all to win a race.
"You are you and I am me. Together we are one." --AM