Long post here. tl;dr at the beginning:

Are the DCA Aeon 2 Noire, or headphones for around 1.000€ in general, worth it in terms of sound quality compared to headphones for around 200-400€? Are the DCA Aeon 2 Noire a good everyday option for fatigue-free listening with a "high-end sound"? Also, how do planars compare to dynamics in general?

I have acquired a few headphones by now and wonder what "high(er) end" headphones, especially the DCA Aeon 2 Noire, offer compared to headphones around 200-400€. I am somewhat looking for a neutral sound, but with more bass than the HD 600 (but not bassy) and good detail retrieval and highs, but no peakiness or treble that gets annoying after some time. I guess I am describing neutral to the Harman curve here. I basically want a headphone for every day, high quality, fatigue-free listening. At this price, I am also looking for longevity, if these would break five years after buying them I'd be pretty upset. I am not expecting a Beyerdynamic level of serviceability and replacement part availability though.

My questions are: Are headphones for around 1.000€ worth it in terms of sound quality or are we just talking about "different but equal" here? How does a planar sound different than a dynamic in general? Are the DCA Aeon 2 Noire a good option for what I am looking for or should I get something else, even more expensive or way cheaper? Should I just get the AKG Samsung K371 instead because I am probably looking for a Harman neutral closed back? Are the DCA Aeon 2 Noire good at all or are there any obvious flaws?

For reference, these are the headphones that I currently use/are in my collection:

• Sennheiser HD 600: daily driver, I really like the neutrality and intimate vocals, but sometimes they appear a bit boring; as in: "This is great, but a bit more fun would be nice"
• Beyerdynamic DT 1990: used for "active listening" (= "analysing" the music and looking for new things) and gaming. I really like the bass with the balanced pads and I also like the treble, but some days they are too aggressive and too attention-seeking. These are usually what I put on when thinking "This is great, but a bit more fun would be nice" with the HD 600. Most used after the HD 600.
• Audioquest Nighthawk: used for relaxing at the end of the day and while studying for background music. I actually like the sound, the darkness is great for some genres but horrible for others, nothing for every day. Second most used after the HD 600.
• AKG K712: used when I want the very wide soundstage or when I want something different from the HD 600, but not the treble of the DT 1990, also for gaming. These are just one-trick ponies for me, I like the soundstage but compared to the HD 600, the DT 1990 and the Nighthawks they just seem lacking when it comes to everything but soundstage, putting them on is somewhat hard to justify for me.
• Beyerdynamic Custom One Pro: used for commuting (especially in winter) and for long study sessions at university, also when I want closed backs for better isolation, sentimental value as these were the first headphones I bought with my own money. I like the bassy sound signature, as I am not critically listening when using them anyways. Used under certain circumstances.
• Grado SR80e: used when I actually don't want bass, but want to focus on the vocals and/or the treble, when I want to listen to jazz, but don't want the darkness of the Nighthawks, don't want the bass of the DT 1990, don't want the big soundstage of the K712, yet the HD 600 seem too boring and I want something with more "sparkle"/highs. Used under certain circumstances
• Sennheiser HD 25: used when the COP is too big or when I will get sweaty, e.g. while mowing the lawn in summer or working out. I like the bass for the slam(?), and the overall sound for being non-offensive/somewhat neutral. I don't care for how these sound as they are only used under certain circumstances.
• AKG K240 Monitor: bought it some time ago when first getting into headphones, I don't really use them, but I keep them for somewhat sentimental/archival reasons as I am from Austria and they are a quite successful Austrian product that was used in basically the whole world. These sound very aggressive. I don't really enjoy nor use these, but I keep them anyway. Used very seldom.
• Superlux HD 681: bought it some time ago when first getting into headphones as they are rightly praised for being very good value, nowadays I'd offer these to guests if they are not into headphones and need headphones for some reason. They sound really good for the price, but I have better things now. Used very seldom, I'd probably give these to a friend or family member if they want them or need headphones when getting the Aeon 2 Noire