...until I see some actual evidence such as spectral analyses showing a verifiable difference I'm going to assume most overpriced products are snake oil, at least with more simple parts like cables.
I couldn't agree with you more. However, some clarification is necessary. Let's not loose sight of the fact that The signal that is sent through these, or any other cord/cable, is not sound but electricity. That's right, these signals are simple electrical impulses. While l will be the first to admit that I do not know as much about sound as I want to, I
do know something about electricity. (or, in this case, electronics)
Electricity takes the path of least resistance. That means that the best cable is one that has less resistance to electricity while at the same time is robust enough to stand up to the rigors of some schmo tugging on it and mistreating it. For a moment look at it like a garden hose. A hose with a larger diameter will allow more water to flow through it. In comparison, a cable (or wire or cord) with lesser resistance will allow more electricity (or electrical impulses)to flow through it.
What is mostly used for guitar cables is called shielded coax. This type of cable has a center lead (or wire) surrounded by some type of insulator which is in turn surrounded by a shielding which is then surrounded by an outside insulator which acts as a protective shield. The center lead is usually (but not always) a solid wire that is used for the positive (+) signal and the shield is usually (but not always) woven like a basket and is used for the negative (-) signal. Using the garden hose analogy above one would think it would be better to use a very large center lead and a solid shield. The problem with this is that the cable would then not be flexible. Here is where the difference in good, better, best, and monster arises.
People (including cable manufacturers) have known for a long time that the electrical impulse going from an instrument to an amp will not ever be above a certain magnitude. Therefore, guitar cables do not need to be greater than a certain diameter. You reach a certain "good enough" plateau and beyond that is useless and overkill. Remember, we are not talking about sound but electrical impulses. Sound does not travel through these cables. The best cables will use the best materials but the diameter of the leads will pretty much remain the same. The best cables will have a better outside protective shell.
So why are Monster cables better? IMHO they are not. One would think that producing and selling a cable that is in the better category but charging best prices would be good enough. Maybe so and maybe people would forgive and overlook the markup but that is not the case. Monster offers cables that are consistently in the better category and sometimes in the best category but charge prices that are ridiculously over inflated.
Back when I was an audiophile I used a lot of cables that had RCA phono connectors on the ends. Several times I tried Monster cables but found them a little "weird". The cables were thin and did not stand up to constant usage and the connectors were overly large and bulky. I tried Blue Jeans Cable and have not gone back to any other. They custom make cables to whatever length you need. I found that, even with their best Belden cable laser welded to industrial RCA phono connectors they were consistently half the price of the bottom of the line monster cable and so much better quality.
Monster cables have left a bad taste in my mouth and I will not ever use them again. For what they offer, they are way, way, way too over priced.