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

One consideration NEVER looked @ IMO is the FOR SALE market...Too little attention is paid when choosing a component to how many units are active on the for sale market & how many have been sold in the past few months..
 Look at mass produced speakers like KEF,HIGHLY touted by Pro reviewers and the forums BUT if you look at the current market & past 3 months you will see they are the #1 most flipped speaker available today..Some will argue that’s because they are also #1 purchased but that just makes my point..There is a reason they are flipped more than any other speaker..
 When I choose a component,I want to know people that have bought that component before me are holding on to them..Look at speakers like Reference 3A,Harbeth & Spendor..For every 1 for sale now or sold in the last 3 months there are dozens of KEF,Monitor Audio,Klipsch,JBL & on & on...

@kofibaffour you completely missed the point of OP's thread..