Welcome!
I gotta second Daniel, Honda did a pretty good job of tuning the VX in for maximum mileage. If I were going to tweak one, I probably wouldn't fiddle with the exhaust.
The VX is pretty popular in these pages and there are some guys here who are whistling up cartoonishly good numbers. In particular look at
MULE VX, which points up just how well the gearing and torque optimization of the VX rewards weight reduction and serious aero mods. Donkey gets such great mileage, he is literally going well over a month between fills.