Just sharing MO, not well rounded replies though :
- Depends on you. If you have made up your mind not to use CNG ever again then sell it. No idea about the probable price though.
- Being resident of KHI, have not much idea about the demand in those regions. But, my intuition says that you may get better value in your city i.e. central Punjab.
- There is no definitive answer. It's purely a subjective matter. Some buyer prefer Non-CNG'ed engines, some don't.
My conclusion would be that if you plan on selling the car in near future and you don't need bit cash right now, then keep the kit with yourself and sell it while you are selling the car. So, if the buyer wants it, sell it to him if he doesn't sell it separately.
When I am looking for a used car and someone tells me that the car is used on petrol, but, it's CNG'ed as well or at least once was, I never believe the statement . No matter how I am rocking my head to show my approval, but, inside I am like give me a break :P. No offense intended or implied to anyone, just MHO :).