Fuel economy is definitely not the strong point, due to the physics of the long combustion chamber etc. Having said that when my scoob was tuned to the same power as a standard RX it had the same fuel consumption so go figure!
Plus when adding forced induction there is the negative perception introduced by the rebuilds at low-ish mileage (non-turbo engines go on for the kind of mileage you'd see in boingers). Although that has so much to do with how they are looked after (or not)...