That's been my experience. Oh you might think it's gone, but it comes creeping back. Smoking in a car ruins the car. Of course some vintage or collector or otherwise expensive newer cars, yes it will be worth it, maybe back to metal restoration. And this is NOT saying the mentioned techniques and products don't work. I say go for it, and agree with the process analogy mentioned by the pros. Just keep at it. You can get it quite satisfactory.You'll never get rid of it. It gets into all the vinyl wiring insulation and anything else that's permeable.