Washing the car does not affect tint in any way, no matter how long the tint has been on. I tell people not to clean the inside of the glass for 3 days.
As far as water spots on the glass, a quick pass with a mild polish works great for me, followed by a layer of wax or sealant. I don't put wax on the windshield.
Constantly cleaning with ammonia-based cleaners will cause the innermost layer of the film (the scratch-resistant layer) to dry out and it will start flaking like dandruff. Periodic cleaning with ammonia goods is fine.
Vehicles with factory privacy glass offer no benefits other than a little shade. There is no heat reduction, no UV protection, and in the event of an accident, the glass will shatter and fly everywhere. Aftermarket window film will reduce the heat coming through the glass (it's still going to be hot in your car if it's been sitting outside all afternoon), it will keep out 99%+ of UV rays, and it will keep the glass from cutting you like mad Ginsu salesman in a colllision.