Does having 32GB of RAM use significantly more power at idle than 16GB?

No. The difference in idle power consumption between 16GB and 32GB of DDR4 or DDR5 RAM is negligible — usually less than a watt at the wall. Modern RAM is very power-efficient at idle, so the extra modules add just a tiny baseline overhead. The bigger power impact comes from workload, not capacity. Don’t let power concerns stop you from upgrading.