Dear you are not drilling holes into someone's soul. Its a 2009/10 8th Gen, drilling two holes, treating it with paint and professionally applyin the spoiler WILL NOT harm the vehicle and neither the resale. I believe your RED MAMBA deserves the low winged spoiler (NOT the high winged Mugen one).
As for the wheels, I strongly suggest, upgrade to 16" or 17". I was a big denial of the 17" wheels but that's a different story (I am using 225/45-R17). I still have my alloys and new Michelin 205/55-R16 tyres stored. Look, with this colour, body kit, red emblems and other mods in the pipe line with your Red Mamba already turning heads, there's no point in sticking with the Oriel Rims. Loose them. Viper's rims (5-Spoke OEM Jap) are available with a shopkeeper here but that ***** is not giving them below 32K. I know he'll let them go for 30K when I make him smell the fragrance of greens but then the cost of shipment has to be borne in mind too.
As for the tyres, I would suggest go for 205/55-R16 nothing more, nothing less. Don't overpay for brand names like I did in the case of Pirelli and Michelin unless you intend keeping the car for a while and driving for another 35000 KM or more. And nothing drastic is going to happen with your suspension provided it is already in good condition if not great during these 30,000 KMs (Inshallah)