Unplugging power cords from amps/ pre amps

Yes, either is fine.  What wears when done too much is the springs in the female sockets, either on the wall or in the unit.

Any unit with a remote or those with low and high power states may have current flowing but at such a low current it's relatively safe to pull them.  Having just gone through a close thunderstorm I do _not_ do this however and rely on the switches in my conditioners when I'm around.  I'm not always around though.

I wrote about this practice a little here.

IF your system is plugged into separate circuit(s), (as it should be) simply turn the breaker(s) off, back on after storm passes.

WHY would you unplug if the circuit is off?

IF your equipment is plugged into a protective device, either trust your protective device, OR, unplug the protective device, thus everything plugged into it is unplugged.

In your case, or if you do not want a protective device, a high quality plug strip into your separate circuit(s), outlet end located where you can reach it, plug/unplug the pieces there.

I mistyped,  I meant to say:

What wears when done too much is the springs in the female sockets, either on the wall or in the cable.

Not sure lightning will be stopped by a 6mm gap in a breaker. 

IF your system is plugged into separate circuit(s), (as it should be) simply turn the breaker(s) off, back on after storm passes.

My Coda manual very specifically states to disconnect the wall connection before disconnecting the cord from the amp. Connecting is the reverse of that. If the main switch on the back is off, it probably is not an issue, but it is easy to forget this step. The result can be arcing when plugging/unplugging a live cord into the the amp.