Hi snow_fox,

I've spent a fair bit of change for this so called 'audiophile' gears, and first off let me say that there are LOADS of snake oil sales tactics and products in this product category.. so you have to be really wary to find good sources of information. Prices don't always equate to good quality as these parties can be really really bold (in what they claim and how they price their products). With that out of the way, I'm gonna try to answer some of your questions with what I've experienced so far

A. Yes. Probably the easiest property to discern that the high end headphones can bring to the experience is they can reproduce the extreme ends of the frequencies better. Most cheap earbuds cuts off the very low frequencies (<100hz) or high freq (>13000hz?) that takes away the bass punch and crisp percussion effects. Other than providing a 'more complete' frequency range, they should also reproduce it in a more balanced way. Some other more subtle properties that will be improved: better sound stage, more accurate imaging\positioning, more details across the frequency (better resolution?).

B. No. You should try to understand why you're playing the music loudly. If it's too boost a certain frequency that you enjoy from your genre (ie: low\bass for synthesized\rap\house\, mids for vocals, etc) then you should be looking for a headphone with that characteristic in the first place or play with an equalizer. If you're trying to get more 'details' from the music (ie: easier to listen to the lyrics), then a good pair of phones with good details and balanced presentation will also help you enjoy the music at a lower level. In general you shouldn't listen to your music too loud in any settings as it's detrimental to your hearing in the long run. A good pair of phones (and properly configured sources) will help you enjoy the most of your music at lower volumes which are safer for your ears.

C. Most 'noise cancelling' products seem to introduce its own negative artifacts from the noise cancelling mechanism to the music. Afaik it's not a popular brand among 'portable audiophiles' either.. some of the more popular ones I've seen are: shures, sennheiser, AKG, Beyer Dynamics, audio technica, etymotics, ultimate ears, and many more.

Maybe if you share a bit of the genre\type of music you'd like to hear it's easier to look up for the popular phones for said genre in the price range that you're looking for?