I've been a long time user of the 'performance' fuels and think they are worth the extra if you have a performance car.
I think it also depends on what your car has been mapped for too - don't the Golf GTI's have a little label with 98 RON or something inside the filler cap? I had a Clio Sport 197 (with a label on the inside of the filler asking for 97 RON) before my current GTI and a few owners reported worse MPG on standard RON, enough to justify using super or better!
Even my mums diesel festa sounds smooth on v-power