as one of the commenter pointed out about bad programming habits with PHP, a framework will give you guidelines on good coding practices. It'll also help you develop faster and it's also quite easy to integrate with the front-end. CakePHP is like Rails framework but for PHP
I made a post about our switch from wordpress to frogcms... and why we use it. (http://www.pigmata.com/post/website-realign-switch-to-frogcm...)