What is the most overlooked consideration?

Musicality. The gestalt of the component... overall presentation. It is too easy to concentrate on fine details, transients, micro textures, width of the soundstage, image size, etc, and completely miss stepping back and considering if it creates compelling music. 

I have owned high end / audiophile audio equipment and home theater components for fifty years. In that time certainly owning many more than 100 components and only two needed service of any kind (one audio and one home theater). Many pieces of equipment I have owned for over twenty years. 

I’m typically looking for technical innovations that might raise the bar.  Other than that I always look for good value delivered and take resale value into account.  Also always consider how well any new component will integrate into the room and system.  

Looks also matter. 👌 

Your room/speaker coupling and treatment is more important than any fancy cable, amp, DAC you'd ever buy @2psyop 

Chasing anything else is just a futile self convincing that leads to a loop of purchasing syndrome