Storage boxes. Can I discard high end shipping boxes, and still sell in the future?

I would add: original packaging is generally safe but easy to use new packaging that is just as safe. It just takes time and material, and likely ends up a bigger volume due to double boxing which will cost more. I boxed porcelain figures that you could drop from the 2nd floor without a scratch. Lastly, most plastic used for packaging are very harmful, never decomposing staff

I'd say sensitive equipment boxes and packing should be kept for shipping unless selling locally. I'd never discard the box and molded styrofoam inserts for my tube integrated amp.

I acquired most of my equipment second hand. 
 

I never gave thought to whether or not it came in it’s original box. Most of the time, it did not. 

The "original box" thing is overblown for most things. it is something people have made up over the years and it makes no difference in most cases. Paying storage fees means you need to think about rearranging your life instead of throwing money away on storage fees, that's ridiculous. If you feel like you may sell your gear in a short time, yeah, save the boxes. I do save some boxes until I'm certain the devices work properly, but toss them soon afterward. McIntosh will sell you proper packaging if ever needed. For other brands you can pretty much just pack them properly if needed. In my case I have an authorized repair facility in town for all my brands so will never be shipping anything out for service. There is nothing on this planet that can't be packed properly for shipping with materials other than the original. This is not 1890, and most everything we deal with is not and will never be collectible and have the box matter.

Also, it's like buying a car. You are not putting the thing through an X-ray before you to assess if it was properly taken care of, so you assess the condition based on a lot of little things. Preserving the box is one of those and as said before, it boosts the price.