I am wanting to add a link class to nav pages on a page-by-page basis and am wondering if there is a way to add this via a boolean checkbox (or any other method, really)?

Sure you could use a checkbox if there is only 2 states (true or false).

You would need to add the database field for it.

static $db = array(
'ShowExtraClass' => 'Boolean'
);

Add the checkbox to the cms

function getCMSFields() {
$fields = parent::getCMSFields();
$fields->addFieldToTab('Root.Content.Main', new Checkbox('ShowExtraClass'));

return $fields;
}

After running a /dev/build to rebuild the database you should be able to see a new checkbox in the cms and save the value so all you need to add an <% if ShowExtraClass %> in your menu template to conditionally add the class.

Another option would be to have a free text field for entering the class (or dropdown) if multiple classes.

Thanks for your advice - I ended up mixing the two together and using a text field but placing it in the Behaviour tab to keep it out of the content section (in case it gets edited by mistake)

P.S - the above should be

$fields->addFieldToTab("Root.Content.Main", new CheckboxField ("ShowExtraClass"));