Huge mistake, I think...

Think about it this way; your friend has a car which has a top speed of 200km/h and he is driving at that speed but then he applies the turbo boost feature and suddenly the car goes from 200 to 250 top speed. (Your friend had lvl 30 character and he got extra star for him). You are also in a similar car, but standing still engine turned off(level 1). When you turn the turbo boost feature on, absolutely nothing happens (that is because you are level 1). But immediately when you start moving (leveling up) you will notice the turbo boost kickin' in and your car will be much faster than without the turbo boost. If you had not applied the turbo boost your car would be much slower. Now you go 250 instead of 200. Even though the turbo boost did absolutely nothing when you installed it, it immediately started improving your car when you pressed the gas pedal. Exactly the same will happen when you start leveling your character, it will improve much more than the character without stars.