Depends on a few things.
Do you plan on getting another GV250, or are you going to get something else?
This is getting into the "Great Time To Buy(tm)" time of year, so if you were thinking a newer model or different bike then it's a good time to plan that out, & the GV is worth it's box, & that's it unless you want to Ebay it or otherwise part it. (messy and takes some work, but depending on misc factors your $75 would come out of it pretty handily over time if folks still ride GV's to any extent)
If you are getting another GV then for parts will you become a person who does your own stuff. Not all shops will work with your parts bike, & some stuff, like the battery is so close to being done by the time you pull it out yourself that you may as well put it in yourself too.
Misc thoughts.
Even under ideal circumstance, as you note, it takes space. If space is a premium then that's a factor too.
Regarding the box...
If your top box is real cool don't forget to factor in getting rid of the rest of it, but you could argue that since the box is detachable that it's really luggage so should be yours to keep, since it's not part of the bike.
They might be petty and keep the rack/adapter, but if the racks' cheap and the box ain't then you come out ahead.
That's some basic thoughts. There's a bit more too it but I've been up all night and am heading to bed
