Way to generalize. Audiophiles come in all breeds - for instance, I am an engineer/scientist audiophile. Don't lump us all together.
No, you can't hear a difference between this $5000 speaker and this $150 speaker.
Yes, frequently you can. It's ironic that you picked speakers as your example since they are one of the few pieces of audio gear that *will* make an appreciable difference, even to the layman, There is a law of diminishing returns, of course. Additionally, there comes a point at which the sound cannot be said to be "better" or "worse", but is merely "different". BTW, $150 is pretty cheap. Depending on the kind of speakers you're trying to buy, there will probably be a noticeable step between there and $500, let alone $5000.
It is worth noting that the above does not apply to amplifiers in my experience. Well built amps tend to have a pretty small variance, other than the amount of power that they can output or the features that they include (such as decoding for popular surround formats or multi-zone control).
No, these cables don't sound "warm".
Audiophiles of my type (engineer/scientist geek) do often dismiss the high-end cable market as hokum. This is not because there isn't a difference in the electrical characteristics of the cable (there is a difference). However, I am not aware of a legitimate double-blind study which shows an appreciable auditory difference created by cables. Most audiophiles of my type will provide the same (or similar) reasoning. That being said, there is a certain level of cable investment that I feel is justified. For instance, one can possibly use a coat-hanger as a short run speaker-cable without any noticeable difference. However, using that same hanger would probably yield problems if used as a low-level analog interconnect between some source (e.g. a computer) and an amplifier. Because the hanger isn't shielded and that signal is then amplified, the relatively small amounts of interference acting upon the hanger can become quite noticeable. This is especially problematic with long runs of analog video cables. In those cases, poor shielding *will* result in a noticeable degradation of video quality. Generally, I just buy my cables from Monoprice (cheap, consistent).
Regarding some of the colorful adjectives that you often see audiophiles using (e.g. "warm", "bright", "muddy", "tinny", "deep", "full"): they are often shorthand for a particular frequency characteristic. For instance, "muddy" usually refers to an excess of sound in a relatively unpleasant frequency range (mid-bass) between perhaps 150Hz and 300Hz. Describing each sound you hear with meticulous frequency ranges and amplitudes gets old pretty fast, so it's way easier to have a short hand. Some audiophiles go too far and try to use these adjectives creatively - this is not generally helpful, since a good descriptor should be understood by all. Haphazardly using the same BS terms one uses to describe an acting performance (e.g. "luminescent") doesn't help anybody. Audiophiles of my type don't do that. We use precise language to describe sound, equipment, music, and most everything else (it's a trait that's common among engineers and scientists who rely on precision).
So, in conclusion, those who make uninformed, inaccurate generalizations are the dumbest group of people ever. Yes, that includes you (I mean, did your name ever leave any doubt?).