it's not bug abuse because the room value is divided amongst everyone who shares ownership. if that value is still high enough to give everyone royal rooms, then so be it.
What I've seen is that if a single bedroom is worth $roomvalue, if I put a second bed into it and make that an overlapping bedroom, each bedroom becomes worth $roomvalue/4. If I put a third bed into it and make that yet another overlapping bedroom, I now have three bedrooms each worth $roomvalue/4.
From this I theorise that we have "private room" which has four times the value of "shared room", no matter how many dwarves share the latter.
Since it seems a little exploit-y to me to have ten dwarves crammed into a room just as happy as two, I put my non-legendary dwarves two to a room (once the economy starts) and the dwarves who still can't afford ☼11 for a shared 3x3 room with rough walls and nothing in it? They can go sleep in the barracks.
This does have the amusing side-effect of putting all my wrestlers into rooms and peasants into the barracks.
And with regards to the OP, I'd use the artifact chair to make a spectacular office for one of those useful appointees that doesn't require anything more than a meager office. Because, really, they're the useful ones. And the nobles who envy my Captain of the Guard's fancy chair or table? They can go cry in their perfectly adequate quarters. But I'm like that.