Hello, xuexucheng
To understand the current you must think of the input capacitance of the gate/pin.
If high speed voltage variations exist at the gate terminal, then it means that a high-value current is charging/discharging the input capacitance of the pin.
Adding a resistor limits this current.
Noise-wise, having lower current demands, the decoupling capacitors will more easily filter the supply variations.
It also limits the current in case of electrostatic discharge, but you have the internal ESD protection diodes to deal with that.
Considering your design, if resistor count is important, you can try a prototype with out the resistors.
In my opinion if your design is mostly digital, or you just don't really care for an extra stable and noise-free VDD and VSS, it should work just fine.
Lampros