Nothing is so bad that it can't be made worse. I just went through this process without benefit of the advice in this conversation.
Instead, in my thrashing, trying things that might work, I set the default kernel to one of the RPi kernels. This turned out to be a terrible idea, because this disabled Mathematica. The RPi login dialog would come up whenever I tried to start it (I had never been able to figure out what the Remote Development Kit dialog was looking for) so the system was locked into a loop. The program managing the remote login dialog box couldn't be stopped by the Mac's Force Quit, the OK button, the cancel button, or the window close button. Mathematica itself could be stopped in the Mac Force Quit window. The problem infected all versions of Mathematica I had on my Mac, and it persisted through Trashing them all and reinstalling 9.0.1.
While I was casting around Google, looking for a way to avoid reformatting my hard drive, I had Mathematica idling in the background, blinking on and off in the Force Quit window with a "(not responding)" label attached. For reasons unknown, after a long time Mathematica's palettes finally appeared (pink) but the main menu was active. I was able to follow the instructions above, clean out the kernel list and reset the default kernel. A Christmas Miracle? Probably not, but pretty mysterious nonetheless.
So everything seems to be running fine. I'd still like to get the remote kernel running on the RPi, but I'm not eager to start messing with the RDK again.
Has anyone had success setting up the remote kernel from the Evaluation menu?
So far I've tried
Evaluation > Kernel Configuration Options > Add
Kernel name: RaspberryPi
x Basic Options
Launch on x Remote Machine
Kernel program: wolfram
Remote user: pi
Remote host: < my RPi IP address from sudo ifconfig >
Evaluation > Kernel > Start Kernel > RaspberryPi
dialog box opens
key in pi password
Messages window: The kernel RaspberryPi failed to connect to the front end. (Error = MLECONNECT). You should try running the kernel connection outside the front end.
What next? I've been able to establish the link and run wolfram from the Mac Terminal via ssh, but not from a notebook.
Any suggestions would be welcome.