Refer to figure.
A rotating mass, such as a gyroscope, will tend to resist changes to its orientation in space.  This is known as gyroscopic rigidity, the more rigid it is the less it will respond (precess) when subjected to an unbalanced torque and vice versa.  This property is very useful in instruments which need a reference datum such as an attitude indicator or directional gyro.

Factors affecting rigidity:

• Speed of rotation - the faster it spins the more rigid it is.
• Mass - the greater the mass of the rotor the more rigid it will be.
• Distribution of Mass - the further the mass is from the axis of rotation the greater the rigidity.
    

increases the rigidity → INCORRECT.  The faster it spins the more rigid it is.

reduces the rigidity → CORRECT.  Reduction in rotational speed reduces rigidity.

makes the gyro harder to precess → INCORRECT.  Decreasing the rotational speed of a gyroscope reduces its rigidity making it easier to precess.  Precession is the movement of the spin axis away from its original orientation due to an external force.

causes apparent wander → INCORRECT.  Apparent wander refers to the apparent movement of the spin axis seen by an observer due to Earth rotation or transportation across the surface of the Earth.  Reduction in rotational speed reduced rigidity which will cause real wander.