Quote from The Shadow
What he said. The Nether is built with the same seed as the regular world; deleting DIM-1 will reset it from scratch, but won't give you anything new.
If you want a wholly new Nether, you'll have to make a new world.
Quote from thekrimzonguard
True, but if the nether was originally generated in an old version (was it?), then the regenerated nether will be different and have the new features in the same area.