Sure, they make you sound cooler (or dumber) when you tell someone you dropped a grand on cables!
I would say there is a substantial diminishing return on many of the peripheral parts for hooking together the components of your system. I would say for the majority of people that generic/cheap speaker wire -- so long as it is new and has not been broken or otherwise damaged -- is probably good enough.
For those of us with a more discerning ear, it is really a matter of sense and opinion. Many people I have spoken with recommend listening to different cables (or really what ever product you are evaluating) with your favorite music that has a lot of dynamic range (I tend to use Dark Side of the Moon). You can then start to make your own judgments about where on the diminishing return curve you feel the most comfortable as you weigh the cost versus the quality. I personally would never spend $1000 on speaker cables, but I often fall on the lower side of the curve and try to really find the best bang for the buck in all of the hifi equipment I buy. Good luck...
I worked for Huge Cable Corp. a few years ago and got training in the design of their high end cabling. It *IS* better but it's all relative to the capabilities of your ears. We had a sales room that had identicle audio setups, side by side with the only difference, the cableing. Monster cable on one, radio hut kicked ass on the other. And there was a substantial difference in dynamic range, overall gain and top end and low end frequency response. I checked the set up myself and dang if it wasn't real.
That being said, I still have regular cables in my home system.