Negligable, just cools down intake temp so car will be happier, if you upscale the ic you will nerd to do supporting mods too to get the gains, higher boost, largers exhaust output, intake, map ect
Bit of a grey area really this! It's a bit like adding a 4 branch manifold,the gain's are very minimal but does help in the process of power gain! What it really is,is the price of a larger intercooler and manifold compared to the power gain is virtually nothing but does give you something,ie 1-2 bhp more!