One email, adapted to membership status
We have a setup like this. It's possible if you're comfortable with the smarty template language. If you enable the smarty email setting, you can put limited code into your email template that, say, does an API call to see if someone is a member. Then display the appropriate 'block' depending on the result. This works, but is vulnerable to users breaking it if they edit the template. I'm certainly interested to see what other suggestions people have.