What is dendritic processing good for?
Action potentials are always based on coherent synaptic inputs. So dendritic processing means rewarding specific coherent subsets of synaptic inputs. 

So to me it makes more sense to frame dendritic processing as allowing neurons to detect several different patterns (alternatively or at the same time). 

In that case each dendritic spike encodes a different pattern. This allows a neuron to play roles (or maybe the same role) in several different contexts (or possibly in different combinations of contexts). If this is the case the neighbourhood mapping you describe doesn't have to exist (though it still might).