2010-12 was the first iteration, 2013+ is the second iteration for this Gen SHO. Since your test driver was not the intended vehicle of purchase, hard to say whether to purchase or not. You may get the one bad apple in the lot, you know?
H&R springs will lower your SHO and make it a tad faster as it will prevent the car from "squatting" as much as the OEM suspension.
Get good tires on there. What comes with the 2012 you are buying? Depending on the conditions you see, you can pick from Michelin, Continental, General, Hankook, etc.
Braking performance varies, though it was upgraded OEM for 2013. If you feel the brakes are inadequate, flush the brake fluid, and change out the pads/rotors for aftermarket (pads at the very least).