Well. To make more torque you have to burn more fuel.
To make more power you have to either make more torque, move where you make the torque up the rpm scale, or both. Doing both make the most power.
But the higher up the rpm scale you go - the less you have that "easy and smooth drivability".
Plus that mileage is going to suffer.
These two links explain the effects of hotter cams and will give you an idea of the sort of non-stock parts you have to fit to the rest of the car as you go up the power stages.
http://www.hughesengines.com/cams/choosecam.asp
http://www.hughesengines.com/cams/heh_guide.asp
Everyone on this board thinks I must work for Hughes Engines or something. They are the only company I recommend to anyone. But that is only because I think they sell the best product
for the price. Plus their web site is handy for explaining stuff.