These seem like problems with that design, not something fundamental.
Could one conceivably use different materials (that maybe didn't exist back then) resistant to aquatic stress and salt, to have made the old plan much more cost effective?
Following this line of thought I think you wind up with something close to what SpaceX does. Because the next largest save-able cost would be the boat crew to go recover it. So attach a propeller to the rocket to have it come back on its own. Then you want to save that cost and complexity so have it come to your boat with no crew and touch down gently.
Could one conceivably use different materials (that maybe didn't exist back then) resistant to aquatic stress and salt, to have made the old plan much more cost effective?
Following this line of thought I think you wind up with something close to what SpaceX does. Because the next largest save-able cost would be the boat crew to go recover it. So attach a propeller to the rocket to have it come back on its own. Then you want to save that cost and complexity so have it come to your boat with no crew and touch down gently.