I hate to think of the time and material involved - and for what ?!?!?

If you're anything like me, once you start you'll want to weld every seam. I'm in the process now of taking a driver's section floor pan apart to use as a replacement panel and I can tell you that welding the seams on just this one section alone would be a daunting task. In the end, besides a ton of hours, miles of mig wire and untold tanks of gas, what do you have ... a car with not much more structural strength (if any) and one that will be a MAJOR headache should anything happen that requires a panel replacement in the future.

If it were me I'd clean everything as well as possible and then redo all the seams with seamsealer. I also think "today's" seamsealers will do a much better job than the sealers of yesteryear - which had a tendancy to dry out and crack which subsequently let in moisture.