Boxes

Yes definitely, they are valuable. Shipping stuff like speakers gets really challenging without them. Many companies actually have new boxes for old equipment… I think Pass does. 
 

I tried selling some old ugly black ribbon speakers and the cost of constructing shipping crated was a couple hundred dollars. My speakers now have an incredible polished red violin wood finish… with out a single scuff or scratch. I cannot imagine transporting them without the original packaging. 

I don't know about potential buyers, but they certainly have value to you. You need them to ship the speakers.

i agree w @roxy54 

Yes!

I keep every box my equipment comes in, even the small stuff like cables. Especially since I tend to change stuff frequently. 

Just like owning a lawnmower, keeping equipment boxes stopped when we sold our home and moved to a condo. I am just not willing to use valuable square footage for something I may never need.