I agree with most of what is in this thread, and yes, there are differences between IEMs in different price ranges, and usually the higher priced IEM sounds better. How much better is subjective.
It is personal preference/perception if the extra money is worth it to you. If you can audition them with your source/music, that would be the best. What I tried to do was find out who on here hears things in a similar way to me via a review of a product I own. Then I see what they think of other products.
Would you be willing to buy an IEM with a lower sound quality that is more comfortable? How about better isolation for less SQ? And the SQ is perceived.
I first bought some cheap IEMs that I initially thought sounded OK (but not great), and stumbled onto this site. I was looking for $200 IEMs, but read that $50 IEMs that were very close in sound quality to one reviewer (the well respected HeadphoneAddict), so I got those (NE-7). They sound really good. But more reading (when I should have just walked away) made me wonder if these sound this good, how much better would more expensive IEMs sound. So I ordered the IE8s. While waiting for those, the Phonak Audeos intrigues me, so I now have those also.
I can tell you which is more analytical, more detailed, has a wider soundstage, but which sounds better is subjective. Is it worth the extra money again is subjective. I chose 2 different IEMs with different sound signatures because I wanted to hear both, and enjoy things about both. And I want to burn in my IE8 somewhere between 100 and 200 hours before I make any final decisions about which I like best.
Back to the NE-7s. If I listen to the IE8 or the Phonak before the NE-7, the NE-7 doesn't sound very good. But if I just listen to the NE-7, they sound very good. Is the price difference between the NE-7 and other worth it? To me, yes. Are they that much better, to me yes and no.
At least one person on here wrote that once you hear better, it is hard to go back as your mind has expanded.
For me, the process in choosing a headphone (in hindsight) is:
1) What sound signature do you want and what genre do you primarily listen to.
2) What is your source.
3) How important is isolation/fit/comfort
4) What fits the above criteria
5) How much perceived difference is there, and decide on paper, or preferably with your ears which one is best for you.
And also, is it better to expand your budget and wait a little while for something you will like better, and over the long run be cheaper (because you don't buy many new IEMs)?
I think that is more like a quarter than my .02 cents.