Re: 156 tuning and knock sensor
what do you mean by a chip? a remap? you will only get approx 5bhp, and not a lot of difference in performance.
cams cost a lot, but they do make a difference, to get the most from them you really need a different exhaut and intake and them a custom made remap. total cost well over a grand, but you'll knock a second off your 0-60 time.
you have knock sensors but your ecu strategy can only adapt up to 95ron so there is no benefit to running on v power or any other higher octane fuel. this is explained on the shell website. you must have fully adaptive ignition timing (or an ecu map designed for higher octane such as any jap import) to take advantage.
sprint booster is a con, but you knew that already.
best thing to do is get a cat back exhaust (powerflow are cheap), a GSR silicone intake (or make your own), and an ecu remap (£250). combined that'll make a noticable difference without costing the earth.
or even better fit the gearbox from a 1.6TS, then you'll fly without any other mods!
or even better better, do both.