When low use, do I change parts and fluids more frequently than mfr suggests?

Well you shouldn’t have to replace the plugs for at least another 100000 miles. I would increase the brake fluid unless you have switched to full synthetic brake fluid. Coolant interval should stay the same as it mainly time based. Belts and hoses tend to go bad just sitting so keep an eye on them, tires are the main factor as they will weather check over time then become unsafe. The rest can stay on the service schedule.

Spark plugs I would change per recommended miles. Fluids like Oil, should be changed once a year due to condensation. Trans fluid would be per miles. Fluids like brake fluid and coolant should be checked for effectiveness.