Even the soil you put your home on will effect the sound quality. So, you had better choose a good plot of earth for your system. Is that so? Maybe. I determined I would not relocate or excavate my home to find out.
Now, they say the quality of the cable in your walls makes a difference. Is that so? Well, based on my experiences the power cords, power supplies in components, every other cable I have ever used in a system, the internal wiring used in a component, whether one single wires or bi-wires the rig - and now I'm even moving to double true bi-wire, with four pairs of speaker cables - HAS made a difference.
So, the question is, what is it worth to you, and how would you tell a difference if it was not specialty cable? Are you going to build two rooms identical, one with and one without the Over-the-top house wiring to the room? My point is that there are a myriad of influences upon systems, and the wall wiring of course is one of them.
When I built my room custom from the cement pad up I went with heavier gauge romex, but did not seek a custom cable. Was that a mistake? That depends on your perspective. I have built incredible sounding rigs, so I don't think it was. What you need to keep in mind is that if you don't pay attention to the system itself you'll never approach the sound quality of a great rig even if you put the world's best wires in the wall.
I do believe that if I spent a boatload of money on specialty cables for power from the breaker box to the outlets the performance would be much better. But I also know that THE most critical element in cable performance imo is total gauge, so I upped that with marginal cost increase.
When it comes to wiring there is no such thing as a part of the chain which cannot be improved. But it's a cost/benefit analysis for specialty wall wiring if. No matter if you have a $5-10K rig I'm sure the difference would be audible - if you could conduct a direct comparison. But whatever you do, don't be chintzy when it comes to getting your system cables! You absolutely CAN kill a rig's performance regardless of the in-wall wiring, with POS wires performance-wise for the rig. You will be shocked at how poorly some sets of cables perform, while others are astoundingly good.
If I had known two things prior to building the room, my decision may have been different;
I didn't know I would be reviewing
I didn't know how extreme cables influence a rig
I'm very happy I was as radically motivated as I was to build the best room I could solely for my own enjoyment; it has functioned beautifully as a reviewer's space. But, had I known how fundamentally cabling shifts the performance I may have put $500-$1K into better lines from the main power.
It's the kind of thing that if you are hard core, perhaps someday putting in tens of thousands into the rig, then maybe you want to do it. If you are a casual audiophile who will likely never invest more than $10-$15K then likely it's not worth it. You would get every bit as much bang for buck from pursuit of system components, cables and speakers. What you are proposing is for the cost-no-object room/rig. If that's your goal, then do it. Short of that, it's not necessary. But if I were to build again I'd probably put in 8 Ga./double romex? if I could for the component receptacles.
What yo don't want to do is believe those who have zero experience with cabling, who say, "bla bla bla... miles of power lines, transformer, bla bla... the last three feet of cable," in order to dismiss the efficacy of aftermarket cabling. They are completely out of touch with building high end rigs. There are also plenty of hard of hearing audiophiles who literally can't hear the difference and say it doesn't matter.
Well, I say it would matter to do upgraded in-wall cabling. You likely can't demo it, but we've covered the basics in the variables. I did most of the work on my room myself, and it cost me right at $8,000 for the room, including the remote lighting system, solid door, black dropped ceiling installed, etc. So, would I put another $1,000 on specialty cabling for power? No. I put about $2,000 into noise abatement; I went absolutely crazy on materials and construction to make the room like a vault. Trust me, spend your money on that and the rewards will be HUGE, far more critical than the in-wall wiring. My room is one of the best environments I have ever heard music in 25 years, bar none. I've been told by industry insiders that it's like a mastering studio, the noise floor is so low. It also keeps the sound from intruding to my sons' rooms upstairs. Dollar for dollar put your money into the construction/noise abatement. Spare no expense on that aspect of the room and you'll be forever thankful.
BTW, I did upgrade the duplex outlets.
Finally, know that power conditioners/filters, etc. all take as well as give. I've never encountered one which does not absolutely diminish definition/clarity of the signal. They typically improve macrodynamics at the cost of microdynamics.
So, for the most part I agree with the recommendation of the tech; it sounds like he is giving sage advice. In a perfect audiophile world I would put gonzo in-wall cabling in a room. In the real world there's a LOT of variables and such cabling is not necessarily the most critical of a limited number of choices, the difference between hypothetically perfect design and optimization of compromises. :)