I am not going to argue about the choice of a template engine against only PHP. I choose not to use a template engine, like Smarty, because I would like to learn how to prop
What you might want to consider, if you should opt for a MVC-style approach, if you include your templates inside an object (one of its class methods) then $this inside the template file will point to the object you called it from.
This can be very useful if you want to ensure some kind of encapsulation for your templates, i.e. if you do not want to rely on global variables to pass around dynamic data (e.g. from a database).