Personally I certainly tend to agree that the stone-rowing/walking is the 'better' of the ideas for the reasons you give Nigel.
I kind of regard the erection as a bonus (snigger). Not sure it would ever have a NEGATIVE effect on the overall project as you seem to be worrying, but it MAY just be worth thinking about.
Just off the top of me head, could you keep it back as a 'part 2'?