John Snyder of White Ensign Models explained some of the pitfalls of rescaling PE a few years back.
It is not just as simple as pressing a rescale button. Some items drawn for, say 1:350, have been drawn with line thicknesses which will yield cost-effective etching. Any narrower and they may etch through ruining the part (one of the reasons they sell second quality PE sets). When going from 1:350 to 1:700 they do not just rescale the drawing by half. They need to go back and selectively redraw lines to the needed width for effective etching.
Same thing happens going the other way. Small lines at the limits of the etching process may appear too large when the image is blown up 200%. Again, selective editing is needed to narrow lines to appropriate dimensions.
Part layout also gets changed for effective and economical etching in the different scale.
Then there is the selection of different thicknesses of brass stock to etch from.
It is not a press of a button thing. It takes some engineering and design time.
This is among the reason why the railings on some etch sets (thinking the old True Details here) looked like a split rail fence.
And to the point about the piece of brass being twice as big when you go from 1:700 to 1:350 -- the piece is twice the length and twice the width. 2X2 = 4. The new piece is 4 times the size of the original