YES IT DOES AFFECT THE ENTIRE SYSTEM>>>>>>>>>>>>>>>>
Since vaccuum comes from the engine anything connected to it is a leak.
If you are not using the heater vaccuum units you should plug the line going through the dash that feeds them. A leak is a leak and this causes a "Lean mix" on the engine. This sounds like it would be good making things lean but it affects power and thus milage. In extreame cases a lean mix can cause excessive heat at the intake valves as some of the cooling of the valves is obtained by the incoming fuel air mix. You might not see a drastic improvement inmilage but the car should run better with the leaks plugged.
Dennis