The only problem I see with Nitrous is it being a resource that's difficult to renew while on the road. I'm guessing you can't just get it filled at your average truck stop or gas station when it runs out. Being able to make the power without it tends to mean it's on tap whenever it's needed without having to worry about running out of spray, etc... Although technically the power you gain with nitrous is directly relatable to the power gained other ways assuming both gains are otherwise equal, IMO it's much cooler to make the power without spray.