Regulating battery overvoltage to an IC pin
You should always place decoupling caps as close to the chip as possible, after and voltage limiting device.  

A Zener diode would be my solution to protect from overvoltage, but you have to be careful because they do not immediately start conducting at a specific voltage, so there is some range of voltage where the current increases.  So you don't want the Zener voltage too high, but at the same time if it's too low it may be partially conducting under normal voltage operations.  I'm not sure what you mean by using a resistor network with the Zener.  I voltage divider would be good for scaling down a voltage for an ADC or something similar (high-impedance), but if you are feeding power to something a resistor divider is not a good choice.  Maybe you meant a series resistor between source and pin, with a Zener on the pin.  That is OK if the resistor is not too big that it causes excessive voltage drop.

I would place the Zener close to the power source.  As you say there is a common power plane, so put it close to where that source is feeding into the plane.