Good point, but I don't think the value of the end result is necessarily equal to RB, for much the same reason that (I suspect) Shapley value would correspond to (something like) "market value" rather than "market value plus consumer surplus". That is, no matter how badly you want you bathroom cleaned, the value of the labor to clean the bathroom is only equal to the market value of that labor, irrespective of how happy I am to have it done.

While voting doesn't directly map onto a market like that, there is a similar sense in which being one of the voters for something that "had no chance of passing" (thus getting the high margin of victory) is worth less -- even per voter -- than voting for something whose fate was less certain.