Steve,
I think you are over thinking reloading shot shells especially if you have been re-loading pistol and rifle as long you have. I believe it is easier. It is essentially the same as metallic reloading but just using different components. Re-size the hull and de-cap the primer, seat new primer, add powder, insert wad, add shot, and crimp. Just follow the recipes exactly provided in the loading book or from the powder manufacture and you'll be fine.
And the advantages is just like metallic reloading. For 357 Magnum for example you can load 158 grain SWC lead plinkers for the range, easy on the shooter and the gun or switch to full house flame thrower loads with Winchester 296.
For Damascus barrels and 100 year old wood, I like IMR 7625 powder, 1 oz. of shot for my low pressure loads. (5100 PSI, 1050 velocity) So I don't have all this extra powder, I also like 7625 for my plinker 44 Magnum loads using my pre-29 Smith revolver and I get pretty good accuracy from 25 yards. It's dirty and smoky but the clays or the birds never knew the difference.