Well, it is nice when your project to group and it mean not only more money, but more server resources. And if you didn't start to receive money it will be normal if you will start to search for options without increasing monthly payments.
Ever site have content for cache or pregenerate.
Why cache need to be part of optimization? - if you know what you do and how it is very fast way to lower server load. So, after load is lowered you will have time to think about logical optimization ;)
What we can cache?
Drupal(www.drupal.org) is CMS system with very long development history. I work with since 2003 and create many custom modules for my clients, I work with WordPress, osCommerce and ZendCart too, but Drupal is my choose, because it have all what I need and want.