MuchDev

I would create a multiple select page field on the template that you are using to control your navigation. Either point the page field to the parent of your navigational elements or use a asm field and filter by template. Then instead of performing your find on the pages you will just load the field. 
<?php $navigation_elements = $pages->get('/setting-page/')->navigation; foreach($navigation_elements as $elem){ //nav code here } ?>

Are you wanting this in xml, or are you wanting to create an html page, or is this to output the markup for your navigational elements? You could make a recursive looping function and feed it the parent element and in that loop call itself to output what you need from the child elements. There are a couple examples from sitemap examples in Ryans sitemap.xml generator, or my lill guy that I based off his that outputs a sitemap in json. 
Ryan's - https://processwire.com/talk/topic/3846-how-do-i-create-a-sitemapxml/?hl=sitemap
Mine - https://processwire.com/talk/topic/11015-json-sitemap/?hl=sitemap

You could also try out soma's module if you are looking for something already done. 

Let me know if you want me to give you a mod on my function. 

Thanks !!! I knew I'd seen this. I just couldn't remember what this was called. 
This is a great point, I have that module, I'll do this ! 
You are awesome guys thanks for the perfect advice.