Thanks David, good points.
I was surprised since most of the common design tools we use on computers support this with a simple Ctrl-A + edge drag. I guess with architecture it's slightly different.
For sure, I wanted to downsize the square footage, but I wanted all internal walls, doors and windows to scale proportionately. Not just resize the outer left wall to have a very narrow room on the right but all other rooms still the same sizes. In other design tools, there is often even an option to scale the length of a line (read wall) without affecting its thickness. That would have been the perfect solution here, even though the exact thickness of walls isn't of concern to me, as I'm using this just for interior design.
And you're right, I would not have wanted appliances, and furniture to scale down with it, only the building's skeleton. It is exactly because furniture currently occupies a bit more space than it would do in real life that I discovered I had the building's scale wrong!
But I have decided to redraw the whole thing now.
Thanks.