Direct wiring to the wall AC wires?

Why not? If you need to disconnect the amp (for service perhaps) you can always use the plug on the amp end of your fancy power cord. But wait! Why not solder the amp end and have the plug at the wall? One plug either way.

Disconnectable power cords were invented so that manufacturers of all kinds of electrical devices could easily configure their products for sale in various countries having different wall plug configurations. Enterprising wiremongers (sorry about that) saw an oportunity to create a new and profitable product for tweakaholic audiophiles.

If you think that a plug connection on your AC power input is bad the logical solution is to solder the darned thing.
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Dont know what it might do for the sound, but it sure wouldnt pass code any where I'd care to live! Not a good idea if you have small children either...