I'm moderately near-sighted myself and manage to handle VR without any correction, but I suspect a great deal of that is due to the incredibly low angular resolution of the displays. When you're talking about something that's maybe 1/10-1/20th the perceived resolution of the average consumer device with a display, the difference between being in focus and out focus for most people amounts to whether you can discern fine details like the manufacturing irregularities of different subpixels, not your ability to tell what color a particular pixel is relative to its neighbor. I can't speak for cardboard devices, as the lenses and the distance between the lenses and screen is not standardized nor manufactured with tight tolerances, but be aware that those are going to directly impact what your eyes are having to do (or not do) in order to bring the image into focus.
Some nice reading:
http://doc-ok.org/?p=1349 (relating to perceived resolution and VR visual acuity), and
http://doc-ok.org/?p=1360 (relating to VR optics)