Is it good to ground the polygon plane on the routing layer?
It is not necessary to put polygon pours on your signal layers. However, there are a few advantages to adding ground pours.


Ground pours on layers adjacent to the power plane will help with power plane decoupling for high frequency signals >500MHz. Henry Ott does a good job of explaining this.
http://www.hottconsultants.com/techtips/decoupling.html
Ground pours can be used as part of an impedance controlled transmission line called a Coplanar Waveguide.
Adding polygon pours can help balance the copper distribution on multilayer boards and will prevent bowing and twisting of the PCB during manufacturing. here is a link to some good information about this http://www.multi-circuit-boards.eu/en/pcb-design-aid/copper-balance.html
Polygon pours on outer layers can be used for thermal dissipation.