Originally posted by Inaris
standby the system, which puts them at a low spin/near stop
That's not true. The drive is either spinning or it is not. The head requires the full 7200RPM speed, as it is designed to work on a layer of air at the pressure given at this speed. If it went down to a slow speed, the head would have a much higher chance of hitting the disk, which damages the surface.
To the original poster, don't worry about activity, if you look after the drive properly and use it for what it is designed for, it should last forever.