I have the vacuums because they're the single most effective things against cat hair I've ever used--and I tried the competitor's versions because I also thought Dyson was overpriced. After spending $200ish a couple times in a row on crappy vacuums that got clogged I realized that I actually saved time and money with the Dyson I'd had before that, and bought another. Its air path was much less prone to clogging, though I've run into other problems like the brush bar jumping its gearing. Took about ten years for that though.
The space heater and tower fan are hugely overpriced, I won't argue this, in the sense that holy crap, I paid that for a heater and a fan? However, there just weren't competitors I could find that handled 24/7 operation on the oscillator as smoothly and quietly as the Dyson models have. Everything else developed whining noises, stutters, or the air noise itself was too high for usage in my living room by the home theater.
It's true that the Dysons get loud too if you crank them up super-high, and also true that the noise volume tracks airflow, period, and therefore being quieter means they push less than the competition (at least where the competition also buries the turbine motor in a sound-insulated base). The difference is that there is a configuration that pushes enough, quietly enough, which is what I couldn't find elsewhere.
So my bedrooms, where I don't care about that stuff, those get relatively cheap Bionaire or Vornado fans. But for the main room, Dyson actually ends up being worth the money.
Anyway, there's my anecdotal stories as to why in the world I'd spend $400 a pop for stuff that's normally $100-200.
That said, I'm not buying a $400 hair dryer. Jeez.