The Idea is a good one but you should think of getting a ECU to controll when the Spray is used.. Autospeed.com.au sell a smart unit that learns your driving pattern and only uses it when needed as you add a temp sensor to the intercooler and intercept the external temp sensor. I had this installed on my former WRX and it gave me a noticable increase of power in the warmer months. Wont be of much good or use unless you are racing or the Ambient air temp is over 24. May help in reducing the amount the computer retards the Fuel and ignition in summer though.
I am about to fit this same kit to my MCS
and will post results soon with some pics of it fitted. Another good option that is the best by far for a MCS
is to get a water to air intercooler setup. they are the most efficient in a confined space like the mini. http://new.minimania.com
have a unit for sale and I believe there are a few radiator and intercooler manufactures in syd that could make this up for about $1500.00 not sure but thats a ballpark figure i was given.