vasia, consider the following link on
Audio Interconnects which may answer your question.
There is a fairly large industry making these various cables, many of which cost outrageous amounts.
Not as big as you think with the exception of Monster. I don't have dollar sales for companies but it's smaller than it looks. You are quite right. Some cost dearly. Bear in mind that if a person sees something priced too inexpensively they'll associate that with it being crap. Price it higher and it gives a quite different aura.
Obviously people are buying a lot of them for some reason.
Indeed. It is one thing to buy cables on strictly engineering considerations and pay accordingly. Cables are like dishes, silverware, salt, sugar, etc. Come special occasions, you put out your nice china, good silverware, crystal decanters, artistic serving plates that echo the ethnic origin of what you're serving to create a feeling of ambiance. Close your eyes though and the food tastes no differently from Corelle plates you picked up at the flea market. That's cables for you in a nutshell. We live in a free enterprise system and rather liberal advertising and marketing programs. For example you'll see some rather pricy Audioquests that purport to lower distortion. This was recently put to the test over at Audioholics and they found this to be an unsubstantiated claim.
Define the problem. Choose cables that meet the requirements (that link ought to give you a feel for things). Identify your preferences (feel, appearance, locking RCA's, etc.). Pick one.
Can you or somebody else tell me at what level (price, examples of brands) would there be a noticable improvement if I were to upgrade interconnects in my system or essentially cable upgrade over the cheap stock ones is never a good idea?
I think it's good to have the stock ones in a baggie just in case. Generally they are not the most robust of cables but confining myself to audio interconnects, if you're looking for an audible improvement, it's just not there. Again, the original link should illustrate why.
People can, have, and will abuse cables. They'll pull on them instead of gently gripping and twisting the connectors, they'll step on them, and then blame the cable when there's a problem.
For sources, you can turn to RS, the Dayton line over at partsexpress.com, ARs over at acessories4less.com, forum sponsors, Target, Liberty makes some nice ones...so many places and mostly none of them bad.