I'm wondering if there is any way to enlarge panoview in bryce 6?

Both panoviews are fixed size.

The preview in the Skylab is larger than the one in the main waorkspace

If you're interested in a larger quick preview than either of these, go to File - Document Setup 

Choose the smallest size available in the list, and click on the regular Render button.
This will render faster than the full size, let's say 1024X768, change to 256x192.
Once you feel everything is ready, you can switch back or increase the resolution larger than 1024etc.
Remember to save the file frequently and save when you've made the final size adjustment.
Render & Save.

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Ockham's razor- It's that simple

i normally do a  quick render to disc at 72 dpi and say 10 inches by whatever.. without the anti aliasing...basic render options... works for me...