There are some from that inflationary era that are valuable, but in used condition, and to the point where some may have tried to forge fake cancellations, and postmarks. I have a lot from that era, not a shoebox full however, and they're all mint, and therefore worthless. They're not from during the German empire, but from the Weimar republic rather, 1919-1933.
Personally, I prefer the period when things had started to settle down, 1926-27...

I just made a quick scan and processing of a few inflationaries that I have...

I forgot about that used one, top-right, but I don't think it's worth anything. Not all used copies are valuable. At top-center, that's a 20,000,000,000 Mark value, twenty billion.
It's almost unreal that those were actually used to mail something. That's the very reason why many of the used copies are more valuable than those mint.