I have seen a racecar that was sand blasted back to metal, then painted white. It was all done the proper way and the owner was not poor. But only a couple of years later I see rust coming up under the paint on every corner. I don't think any seam sealer was used.
I guess if you do take it back to metal, you need to know about further rust preventative measures. I guess that is what seam sealer is all about. (Sound deadener tar helps also).
I did a lot of welding in my car, with making the roll cage etc. I removed seam sealer to tac weld some seams. It was painted the proper way with 2-pac and etch primer. But it was imposible to remove all the metal dust from every crack and hole. Mixed with a few drops of water and it turns to rust which is easy to see on white paint.
But car preperation can take years if your not paying for it. One reason you don't see guys in their 20's doing Targa or any sort of racings, unless their Dad is paying.
You have to weigh it up. Do you want to spend your fittest years ( 21-35) driving cars, or owning cars that will be good to drive once you are 40.