Importance of power cable for Turntable?

Good point @lewm. It is not a symmetrical situation; if a difference between two competing components---in this instance power cords---is heard, the system is then ipso facto transparent enough to reveal that difference. On the other hand, if a difference in NOT heard, that does not necessarily prove a lack of transparency, for, as you imply, there may in actuality be no difference to be heard.

I would hazard a guess that system resolving power is one of many variables that could bottleneck the performance of a power cable or make differences in cords less noticeable.  I’d think it also depends on how noisy an environment is, how clean the AC input power is, and also how good the regulators are in the components that the cords are connected to.  In a hypothetical (and probably not realistic scenario), if you have a highly resolving system, clean power, no material EMI to speak of, and high quality regulation built into the gear, maybe you wouldn’t notice differences between cords.  Some very high end gear comes with power regulation in a separate chassis.  Is it possible that such components, if implemented right, at least partially negate the effects between a lower end and higher end cord?

I have a VPI Aries Scout and I hired a local dealer who also happens to be a real analog guru to make a house call to set it up properly.  He said the outboard power supply on my particular table was in no way in need of an expensive power cable.  Interconnects are the key and as for the expensive power cable? Better used elsewhere in the system. 

Power cord is an extension of the power supply not of the wall wires. Good well-matched cord will improve the performance of anything that has it. If you can't hear it something is wrong. At higher level one can clearly hear that different cords have different sonic signatures with the same component, not necessarily better or worse. Also, some cords do tend to work better with source components or/and preamp and others with power amps and conditioners/regenerators. My Nottingham turntable's motor has captured cord so I can't upgrade it. Motor controller is a different thing and no substitute for cords, in fact it will benefit from good power cord too.
Anyway, when it comes to turntables I don't know what doesn't matter, it is a very sensitive thing, like it or not or both.

It makes absolutely no difference what so ever. Use whatever comes with the table and spend your money on something more important like a Pizza.