Right, assuming the last answer is out of the question, heres my 2ps worth.
The Airfilter isnt a bad option on the 1.2 16v. From my experience, the standard intake is absolute poo. The exhaust system looks like it should be on a mini too. So youve started in the right place, but I dare say youve noticed little difference. Ive thought about tuning further myself, but as most people say, youd have to spend a lot of dosh on the little old motor to even approach 100bhp.
So, Im gonna go for NOS, or to be more precise N2O. Ive fitted a NOS kit before, so understand them, and my engineer and I are gonna build our own N2O kit. Ive sourced all of the parts needed, and will be able to build the kit for a 6th of the cost of an off the shelf kit (granted it wont be as cosmeticly pleasing). I also have data for IDs for jet sizing and fuel pressure, and we have the kit to set it up properly. Its not an ultimate solution as its not permanent power, but itd be interesting to see what a 1.2 can do the 1/4 in. This way day to day driving wont be effected, and economy will be unchanged (whilst not in use). I can fit the kit in a way that when removed, it will leave no trace of fitting, in the event of it needing to go back to Renault under warranty.