Boxes

I've kept all of my boxes for my current system---I have a few boxes from my vintage system (>30 years old). I wish I had ALL the boxes from my vintage system so I'd say keep them if you can. You can always break them down to save space. 

Maybe speak to your wife tomorrow...

I prefer to buy from sellers who have the original boxes. Buying used equipment is always a gamble and having the original shipping container eliminates at least one of many concerns for me. Others may or may not agree, but I'm only concerned with my purchase comfort.

Flatten them and stack the foam innards to save space, and yes having original boxes is a selling point and gives the shippers another chance to smash the crap out of them.

other factor here is that quite often, in my experience, shippers like ups or fedex will deny customer damage claims if something other than manufacturer's packaging is used for shipping expensive precision items like hifi gear...