The short copy + "Continue Reading . . ." link to a landing page with the remainder of text is probably the best approach. Most of the approaches you'd use on a webpage to supress or hide text will be surpressed by email clients as part of their approach to security.
Before deciding that short copy is better, why not run an A/B test with a sample and measure actualy conversion--not just open or click through on the emails.
You may get more clicks on your "Continue Reading . . . " link at the end of a short email, but if you get fewer that take action at the end of the rest of your copy, you've hurt your overall conversion rate.