The power is controled by your finger and if you know how to use it then it can be an advantage. It does however leave less room for error and the extra power might not be any advantage at all depending on the track they are racing on. If you have great throttle control then more power wont hurt depending on where it comes in on the RPM range but that doesn't mean it will give you an advantage either.

I haven't read to much about engine modding but I'm pretty sure you can change the engine timing a little. I don't think it will give you more power but you can change where the power comes in on the RPM range.

I still don't think modding would be worth it. Power is a very small amount of how fast your lap times are anyway. If you want power for anything it should be passing... if you can beat someone coming out of a corner with more bottom end power then it makes passing a whole lot easier.