The a15 in its standard form isnt a bad performer, but its isnt a deamon. that 80 is what the factory quotes from their test bench and its at the flywheel. In reallity, you could have a motor that performs higher or lower than the rated HP. That depends on many things like machining tolerences, contractor quality etc.

Dont get carried away with spending money on the external bits. If the carb is staying, then its really only exhaust and a good tune.

Yeah maybe 8-10hp which is again at the flywheel, minus the 30% parasitic loss through the drivetrain, and you end up with about 63 ponies at the wheels.

About lightening up, well you may want to consider your local laws about what interior/exterior bits you have to have as minimum. There isnt much to pull off a datto to lighten it up.