Again, the fine folks on #catalyst have helped my understanding. First off, what I'm trying to do is pretty wrong.

Instead of using $c->config, you just need to know that config values are rolled into the object hash during instantiation. So, $self->{foo} contains the config value. (Namespace collisions seem possible, and are on my list to investigate).

# in myapp.conf
  <Controller Foo>
    foo bar
  </Controller>
  
# to use config in Foo.pm
package MyApp::Controller::Foo;
...
sub baz {
  my ($self, $c) = @_;
  # data from config
  $c->log->debug( $self->{foo} ); # logs 'bar'
}
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Optionally, with Moose accessors as suggested in the POD. (And I don't know much about Moose, so this may not be the best way.)

package MyApp::Controller::Foo;
...
# foo accessor 
has 'foo' => (
    is => 'ro',
    isa => 'Str',
);

sub baz {
  my ($self, $c) = @_;
  # data from config
  $c->log->debug( $self->{foo} ); # logs 'bar'
}
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Update: and as I git cloned to suggest updates, I see updates to that section of the POD are already in the pipeline!

Update 2: The POD I should have read the whole time was Catalyst in the Cascading configuration section.