My opinion, and the opinion of my father and the dealers he has spoken to is, that generally, these high performance fuels are useful. Porsche, Aston Martin, and Mercedes in relation to his AMG, they all say that unless you are interested in track or very very performance orientated driving, filling the cars with these fuels every single time is just not worth it. Filling the car with a performance fuel every 1 in 4 tanks is the approach suggested to us.
Another note i would put forward is, that in a 180bhp diesel, will you benefit that much from a 8p increased fuel to justify it? If mpg was improved, i would absolutely agree its worth it, however most studies seem to show that the variations aren't significant enough