theme_hook_suggestions is ignoring my suggestions
You're missing how the framework is designed.

If you're doing anything with hook_preprocess_page() you are affecting the 'page'.

The default template for page is 'page.tpl.php'.

If you want to 'override' this template Drupal needs to understand what's going on so has some conventions.

page--[front|internal/path].tpl.php

page--node--edit.tpl.php
page--node--1.tpl.php
page--node.tpl.php
page.tpl.php


"Theme hook suggestions are made based on these factors, listed from the most specific template to the least. Drupal will use the most specific template it finds"

See: http://drupal.org/node/1089656 and http://drupal.org/node/223440#custom-suggestions

In your case, your defining 'newbies.tpl.php' and expecting this to work but it's still going to use 'page.tpl.php' so to override this you want to do 'page--newbies.tpl.php' (same as 'page--node.tpl.php').

More to the point, you don't even need to set this with hook_preprocess_page() as Drupal will follow those conventions automatically.