Throttle response or MPG could see a measurable improvement. Personally when it comes to plugs, wire, coils unless the system comes from the factory inadequate (not too common) then no measurable gain will be had as long as all those components are in good working order/not worn out.
Once the engine starts getting leaned on and making more power or revving high some gains can be had. Or from my viewpoint+expierences, loses can be prevented.
Genreralzod- it wouldn't be a bad idea to check your plug gaps. Many members, myself included got plugs improperly gapped (some close, some way off). Some have reported better drivability and/or mpg after regapping. .28" for the 1.4T. .32-.35" 1.8
-tyler