de badge? - Free
induction kit? - Depends if you go cheap or decent. a cheap cone filter will gain you noise but lose some power. a good full kit will look better but do pretty much the same, and a aftermarket panel filter in the airbox wont give you the noise but might give you a bit more power 2-3bhp tops anything from £10-150
de cat? - Chances are youll not notice much difference i didnt with my 1.4 but it wasnt vtec. iirc i paid £40 for mine
sports back box? - wont do anything other than make nosie £60-100
lowered? - depends on how low you go. so far will help impove handling but going too far will throw the geometry out causing quicker wear on componants - bearings, driveshafts, cv joints and the one youll notice 1st tyres. also the change in geometry mainly the camber will mean that the contact patch of tyres on the ground will be less £40-1000
larger wheels? - better looking, but you think its slow already add all the unsprung weight and, i think, multiply it by 4.
low profile tyres? - good if your going bigger wheels as will give you a closer rolling radius so speedo wont be out
window tints? - be warned you are only allowed 70% VTL on the front which most are from the factory
are there any engine / ecu mods i can do or should i leave the trusted v tech alone?
dont forget its only a 1.6 so its not gunna be fast, but as i got it free and its like new i'm gunna keep it and get rid of my old fiat bravo 2.0L 20V which is pretty quick compared to this honda civic, but this honda and the two previous honda's we've owned have been superb, reliable and comfortable.
cheers