When resizing a PSD containing linked PDFs in smart layers, the resulting file has bad quality

We have PSDs, where 3 Layers have been added, changed into smart layers, an IN those layers a PDF has been linked and positioned. The resulting smart layers have been transformed in a way that a 3D Packaging is simulated.

So far so good.

Now our customer might ask us to deliver him a much bigger File than previously anticipated. Since the linked PDF is completely vector, you would think: no problem, right?

Think again.

Unfortunately, it seems to me that even if I increase the pixel of the smart layers and the resulting PSD, the quality of the resulting file remains as produced in the first place, but only with more pixels (i.e. blurrier).

This is inconvenient, since a lot of work went into creating and positioning the smart layers.

In my eyes this must be a technical problem or oversight in Photoshop, because one would think that it could take the vectors for the bigger files and render them sharply, but instead seems so rely on the pre-rendered pixels and just increasing their size.

Maybe there is a mistake in my doing, but from what I see it look like the Program PS is playing tricks on us.

Any thoughts? Questions? Tipps?

Thomas.