There would be gains to be had from a remap, but not very much bang for buck wise. You might get an extra 10-20BHP (intake, spacer, exhaust) and upto say 40BHP with all the mods (intake, exhaust, cats, plenum spacer, possible cams, headers, etc), but with a remap weighing in at £1200-1500 (piggybag ECU and mapping), its not a lot, especially if all you have is intake, spacer, cats and exhuast, as the only real performace booster there is the spacer.