Yeah in max offsetting in W is the best, then you can still edit the layout easily, but that doesn't work in every app. Really any app with numeric input for UVs offseting/unoffsetting should be a very very quick task. As you said, scripts make it even easier. So, there are a few things you need to think about yeah, but…
Is there anyway to offset correctly in the W space for Max using the UV editor? I always had to use scripts such as Mesh 2 UV 2 Mesh inorder to push them via polygons into the space, but usually folding them back scaled them in size.
Offsetting has its pitfalls, if you want to move the UV's around you have to take care to make sure the offset pieces are moved also. Which could mean moving the pieces back so they are stacked, then after adjusting them offset it again. Or like Ace said delete the mirrored mesh, arrange the UV's and offset it again. In…