And I disagree with your disagreement!
A vacume is merely the absense of pressure, it isn't a "thing" of itself. There is no such thing as the force of a vacume. It's the air pressure on the outside doing the work, so "vacume assited" brakes is a misnomer, they're really air pressure assisted.
If you want to blast down the interstate all day at high speed, why not get a motorhome? That's what they're designed for. Skoolies, to have any meaning in and of themselves, must be different. They need to take the opposite approach, otherwise its a pointless endeavor. School buses are NOT designed for efficient high speed cruising. They're designed for back road medium speed driving under average conditions. Many don't understand this, get a schoolie, then want rid of it because it's a no good fuel hogging noisey shakey and dangerous high speed cruiser..
Go ahead and spend a few thousands on that old bus only to find later that nobody will buy it from you, 'cause they want a real motorhome.
Air brakes are mandated on trucks due to public safety issues and the irresponsibilities of commercial drivers. If they were so much inherently "better", then they would be on cars, too, right? Wrong, they will never be on cars, don't need all that stopping power. You would probably put air brakes on your moped, cause they're so much better.
Airbrakes unnecessarily raise the maintenance cost of the vehicle. It aint the shoes, it's the cost of fixing problems when they occur, like air leaks and compressors and such.