I have no way of knowing what is wrong. Sorry. And I don't know of any tweaks other than trying another wireless channel which you probably can't do since it's not your router. Whether it matters or not, I can say that the Fedora Unity stuff is a little old and falling behind. For example, it still refers to the deprecated file /etc/modprobe.conf. However, the rest of that b43/b43legacy stuff there is correct.
Some BCM4306 chipsets use b43 and version 4 firmware, and some use b43legacy and version 3 firmware. The kernel is pretty good about loading the correct module for detected hardware...
But it's usually our job to acquire the correct firmware. The Fedora Unity tutorial mentions divining from dmesg output which firmware version to use. Okay, but basically, if b43 was loaded, use version 4, and if b43legacy was loaded, use version 3. The firmware files mentioned in the Fedora Unity tutorial are still good today (I use them, too).
Another thing that Fedora Unity doesn't mention is that some Broadcom chipsets (including my BCM4306 versions) can use the OpenFWWF firmware that comes with Fedora nowadays. Its a package by the name of b43-openfwwf. There is at least a chance that your device would work with that. About the only way to tell is to try it. If the wireless card was connected and on when Fedora was installed, then the firmware package may have been installed. Otherwise, it needs to be installed. You can check for it...
rpm -q b43-openfwwf
If it's not there and you want to try it, then install it and reboot or restart NetworkManager. But just know that if it doesn't work with your version of BCM4306, it may bust what you have working now. But you should be able to backtrack and re-install your firmware again. Just FYI. No promises. At all.