Again, what's the valuation of Intel if (in the future) we see them churning out the same 1GB NVMe cards at the same cost with the same performance? The valuation of Intel and every other tech company is based on future growth potential.
However, the planar silicon scaling is what primarily enables cost reduction for production. I expect the (total device) density to continue to increase with the 3D tech, but cost will go up with capacity increases. Maybe not linearly though, because you don't have to pay for extra packaging.
The 3D memories will probably see some planar (x-y) scaling, they just don't need all of their scaling from it. 3D scaling will still increase bits/die area, and thus reduce $/bit. If doubling the stacking height doubles capacity but adds 30% to wafer cost with extra processing steps, its still much more efficient than 100% cost for two wafers of the previous design.
Scaling efficiency shouldn't be too dissimilar from planar scaling, at least until the next wall is hit.