Any increase in hp, will have an equally detrimental effect on fuel consumption. Logic dictates, if you are pulling and pushing more air in and out, you must therefore add more fuel to compensate.
Of course it depends how heavy you're right foot is.
If you are bothered about the money to swap to a 16v lump, then turbo charging is not going to be for you. If money is no object, stick a supercharged hayabusa engine in the back and wave bye bye to about £5000.
Otherwise keep any mods to within what the ecu will run and enjoy centodom.