For me the only thing that makes the DAP worth it, is not having all of my library stored on my phone. But I travel only a few times a year where if I really wanted more music I’d just would some stuff off my phone first. I’d say it just depends on if you actually think you’d use it over other devices you already own. For me the answer is very seldomnly
Ideally you can have a headphone that excel at something better than others for certain genres. For example, 2 headphones I frequently use are the ZMF Atrium and ZMF Verite Closed. When I want a warm bassy head headphone with amazing soundstage I’ll go for the Atrium. When I want better imaging and a more neutral sound that still is very lush I’ll go for the Verite.
In my collection I also have the Focal Clear MG, Arya V2, and a Modhouse argon.
That said, I like to keep the clears because I find that music that wasn’t recorded well can still sound great on it. The Arya V2 is when I want some spicey treble and it better for certain genres.
That said there has been plenty I have sold/traded. And largely it’s because I found something better in the models I listed above. So with that said it depends on use case. For me I love the hobby and like having options, every once and awhile I will downsize to try new things.