Wow - so somehow this thread got me looking into the G+ settings page again, and viola!  There it is, an option to get notifications at an alternate email address.  Again the convoluted account management rears its ugly head and I have to add my alternate address again, even though it's listed in my main account settings.  But whatever, this seems like it should do the trick.

I still can't set my account 'primary' address to what I'd like.  But perhaps this will resolve my issue of not getting notified of G+ posts?