Free popcorn!!! :D

Great gag. I love it.  
Though I feel compelled to mention, it’s most likely the seal on the scrolls that cause them to be transported when burned and not Spike’s flame. When never see anything but those scrolls be transported that way. It would also make it more practical if the magical seals transported them to the recipients designated fireplace (except Celestia for some reason. Maybe she doesn’t spend a lot of time near one), this would allow an extensive email-like system for those that can afford to have it set up. Spike just happens to be Twilight’s ‘fireplace.’

And in a couple of centuries, invading armies well beyond the borders.
 
“Princess, you’ve uh… redecorated. The, um, the thousand burned skulls of the vicious wolf-soldiers are, ah… a, uh… … …nice touch gotta go.”

I can imagine the stuff that gets accidently sent to Celestia. Logs, marshmellows, burger patties…

Look on the brightside, free midnight snack!