It's not a con - they're hardly going to publish a list of cars and the associated power gains. 5th gear showed tonight that, depending on what kind of car you drive, you do get more power using premium fuels.
Renault probably recommend 98RON for the 182 for a reason, and whilst the difference is probably hardly noticable, I expect it's there.
As for the cleaning effect, the premium fuels do contain cleaning additives and over time a cleaner engine will perform better. Having said that, you probably don't need to use a premium fuel on every fill to keep your engine clean.