bhai, don't ask for advice, most ppl here will tell you to sell it in lower price, while when they sell their own car, they will demand like it has diamond coating on it : )
check the used cars market, or even online what ppl are demanding for GLIs.
total genuine cars are a rare piece these days, so the demand would also be high ... i think u can safely demand somewhere between 17-18+ for such car (provided it is Lahore or ISB reg.car) ... rest ppl will offer and then u can let the market decide !