Is the strength of presynaptic stimulus on the postsynaptic neuron affected more by the dendrites, or the cell body?
It depends on the type of axon, of course.
In Axosomatic synapses the properties of dendrite is not important, but for Axodendritic synapses, the properties of post syn. dendrite is more important as the amplification and other processing happen there. However, Soma is much nearer to Axon hillock, so changes by Soma wouldn't be declined as the impulses won't. It may be depended on neuron properties itself and so that's wrong to generalise!