Thanks for the replies all, and thanks for the pictures Richard! I agree with everything being said; I am using the Zero as my primary/only vehicle, replacing an electric bicycle, which I did have a rack and a huge basket on. I went through approximately the same thought process there, but I think of that bicycle as a much more utilitarian vehicle than I do the Zero.
I do agree that boxes make the bike a more practical vehicle, but as long as I can have my cake and eat it too, then I would like to continue doing that.
I am not worried about what others think as I see plenty of motorcycles with top boxes, and I still think my Zero with a top box would look a thousand times better than the vast majority of 800lb Harley Davidsons I see around. I just still have a mental block about putting a big box back there. Right now I am using a backpack and haven't yet had a situation where that didn't work, EXCEPT picking up takeout that doesn't come in a bag. The other day I rode with a Papa John's carrying bag (the same kind the delivery guy has) on my storage tank and around the handlebars, and while it worked, I was nervous about how close the edge of the bag was to the kill switch, so I decided it was time to find another solution.
The rack will not change the aesthetics of the bike much, but should allow me to put a pizza or other food back there, cargo netted down. I'll continue to use the backpack for the other stuff, and if I want to upgrade to a box in the future I can.
And FWIW, I do find the storage tank very useful. I keep my gloves there all the time, and my helmet locked to it using the included tether when I am running in to a store quickly. The only logistical problem that remains is my overpants, which I usually just wear in. I suppose with a box I could strip down there in the parking lot and stash them but I probably wouldn't bother for the short amount of time I'd be inside. If I am staying somewhere longer I'll throw them in a backpack.