Not everything *will* make a difference. Whether you use imperial or metric fasteners to hold down the transformer won't make a difference. Some things will make a difference. Not every difference will have an effect. However, like our bicycle racing example, we might be concentrating on paint jobs rather than mechanical components.
This does of course bring up a complex question; if the rider *thinks* that the fancy paint job makes his bike faster, then this will almost certainly contribute to his belief that he has the best bike for the job, and be a 0.1% contribution to his marginal gains. On that basis, given that hifi appreciation is about perceived subjective improvements, belief plays a big part. If a hifi owner believes that cable supports and shakri stones improve his system, then for him they do, becaise it's about his belief and not the engineering. Again this is like cycling. Until recently TdF racers used to have to get changed after races in the back of cars, in sheds and so on. Now they have proper changing rooms on the bus, showers and comfortable seats to sit in. It's a marginal gain. It makes no difference at all to the bike, but it helps the rider no end. He feels better, so it makes a difference.
Oh, and this *does* work for foo. If I genuinely believe that my packets of fairy dust on my cables improve the system, then for me they do and it's real. It's as real as it needs to be. In that it's like any belief system. Christians believe that their god gives them strength and support, so they feel stronger. I'm an atheist, I'm on my own. So when the chips are down, one of us takes comfort from a diety, he can do it because God's on his side but I'm out there in the wind. So who's the mug now?