Is there a place to look for general guidance on the attributes that make something worth trading? Like I don't have any idea which things matter and which don't.

No idea Bru

Legit dueling section is a good start.

Example, the zeal community starting new ladder on RoTW here:
https://forums.d2jsp.org/topic.php?t=108944432&f=147

Example: You might shrug at gore riders, but 200% perf upg still holds value.

There are multiple pvp communities to scout in that section, gl.