Don't completely discount enhanced gasoline detergency. Look up Top Tier gas- there are differences between fuels sold at retail, and I respect Shell for consistently trying to differentiate it's products in language that laypersons can understand.
There are even differences in detergents. While all that I am aware of are N based, some older technologies may clean injectors at the expense of increasing combustion chamber deposits. Some more advanced chemistries may claim to remove CCDs, but from the data I've seen the effects are modest. Secondary claims on mileage- or power improvement are sometimes made for detergents by inferring IF a car has very dirty injectors then cleaning them will produce slight but measurable improvements in performance. In practice I suspect most of the folks who are interested in performance hop-ups from fuel additives don't have dirty injectors that the products would be effective on. But heck, everybody has to make a living somehow . . .
In any case, gasoline detergents are effective at very low treat rates (ca. 10-50 ppm Nitrogen if memory serves). So treat rates can be boosted significantly without drastically affecting the other fuel properties.