First of all, it's an ID P - the P stands for "permit." It's not a license.
Second, and more to the point, you have it wrong re the reason you get the IDP. It's not for the rental place - the car (or scooter, bicycle or donkey) rental places don't give a flip about whether you have an IDP or not.
You need an IDP for the police, not for the rental guys. If you get stopped by a cop (or even worse, if you're in an accident - a great risk on a scooter, by the way), the police will want to see your IDP. The rental guys don't care, it's not their problem if the police stop you, that's your problem.
If a drivers license is required to operate a motor vehicle, then you should have the IDP.
I am constantly amazed that anyone would spend thousands of dollars on a foreign trip, then balk at the idea of dropping twenty bucks down at the AAA office for an IDP to improve their experience if/when they get stopped by a police officer overseas. Do what you think is best for you, but I can tell you that when I've been stopped by foreign police officers (and I have been, several times), things went smoothly (and I was let off with no ticket and no hassle) after I handed over my IDP along with my US drivers license.
Be careful with that scooter.