Limiting logic gates input current with serial resistors reading their electrical characteristics
You are mixing up two sets of ratings. The table part of the data sheet is showing the maximum input current you could expect to see if the part was powered from an 18V supply with inputs in a normal range within the supply voltage levels. In fact for that test case the input was set at 0.18V. This current spec is really a leakage current which is mostly due to the input protection diodes on the part that will have more leakage as the voltages increase.

The MAXIMUM rating section where it shows the +10/-10mA input current limits is what the manufacturer says is the maximal current on a single input that can be allowed before the part becomes non-functional. This will only likely ever occur if the input protection diodes on the chip start to become forward biased (i.e. the input voltage approaching VDD+0.5V or GND-0.5V).

If your system design is such that you can assure that your inputs to the logic device will stay within the power supply voltage range then there should be no need to put resistors in series with the inputs to the chip. On the other hand if your inputs may have a tendency to go outside the supply voltage range by more than a few tenths of a volt then you will want take steps to protect the chip. One way is to design the input signals with clamping circuitry that keeps the signal levels from going too high above VDD or too far below GND. The other thing that can be done is to add series resistors such as you are asking about. The resistor value that you select will depend how much the input signals disobey the supply voltage levels. The selected resistor needs to make sure to limit current into the forward biased input protection diodes on the chip. Clearly the best is to limit to less than the +10/-10mA maximal spec. A good operating choice may be +1/-1mA.

The series resistors can be a disadvantage for some applications where the chip is used for high frequency signalling. The inputs to these chips exhibits some capacitance and the series resistor forms an RC circuit which slows down the signal arriving at the chip.