If you have a drawing at 1:100, and want to scale it to 1:200, just drag a marquee around all the symbols, excluding the viewport, and scale it by .5. Text, unfortunately, will have to be changed manually. Do not group before scaling, or you'll loose all layer info. Once that is done, you can re align all annotations with the viewport.
If some dims and notes "stick" to the viewport, you can break that link by cutting and pasting the offending viewport.