The reasons other fluids are changed is due to contamination, dilution by undesired elements (like combustion gasses), breakdown of the fluid’s molecules due to heat and mechanical stresses, depletion of additives (such as the anticorrosives in coolants), and the possible absoption of moisture resulting in icing (such as brake fluids). Power steering fluid is not subjected to the possibility of system failure dues to any of these conditions.
But I support changing it occasionally, using the turkey baster method. Whitey might be right, fresh fluid might help preserve seals and at least it won’t contaminate them. It might even better preserve the pump, since it does lubricate it. The good news is that PS fluid regularly circulates though the reservoir as the pump runs and it’s an unsealed system, which means that the turkey baster method DOES work. Most hydraulic fluids don’t constantly recirculate through their reservoirs.
Go for it.