If I do that, then /usr/local/lib/virtualbox/VBox.sh is owned by
root:wheel, but it does seem to work for me this time even though it definitely didn't before until I changed its permissions to
root:vboxusers. It does now have world executable permissions set. So, I don't know what the deal was. But it seems to be working without problems now, whereas it didn't before.
I don't know, but I'm not about to blow away my system just to check.
I would assume that the menu runs /usr/local/bin/virtualbox which is just a link to the script. So, if you were going to have problems with the script, you'd have problems with the virtualbox command and thus presumably the menu. Personally, I start it via the virtualbox command and not directly via the script, but if you're going to mess with the permissions to run it, you have to mess with the script, since the virtualbox command is just a symlink to the script.
vboxnet, yes I have all that it my rc.conf, and it looks like uninstalling and reinstalling probably put
vboxnet_enable="YES" in rc.conf for me, since it's now at the end of my rc.conf, making it so that it's in there twice.