How can I explain the value of the Secure Enclave / (TPM chip) to a privacy conscious user?
Well, Apple has explained the Secure Enclave in various communications. How well the value of the Secure Enclave itself gets across to an end user is debatable and obviously a matter of opinion.

Most end users probably aren't really that interested, they just take it for granted that "it's all good". And Apple has achieved that for the overwhelming majority of users - not just via their communications, but also their actions (e.g. taking on the FBI in court). 

As for those end users who are more interested in the technical side of things, how many of them actually understand the Secure Enclave is another question - but I guess that's what you're trying to get at. :)

In terms of end users, Apple's primary communication channel is their website. Many of the pages on their website explain the benefits of the Secure Enclave without getting too technical or even mentioning it. For example these pages (Manage your privacy, macOS Security) mention it, while the Approach to privacy page does not. But all indirectly explain the benefits of it.

In addition to the above, most of their individual product pages will reference and/or link to info regarding security features, privacy, etc. So, for example, a user interested in buying the iPhone 7 will eventually come across the following quote:


  Protecting Your Data
  
  Privacy and security are at the core of everything we believe. And
  everything we make.
  
  At Apple, protecting your information is something we build into our
  processes from the beginning. When we have an idea for a product, we
  find a way to make it that ensures your security and privacy. It’s a
  value we’re deeply committed to because your trust means everything to
  us. Learn more about Apple's approach to privacy >


As you can see, it's written for the masses in an easy to understand and re-assuring way, without getting technical or even mentioning the Secure Enclave.

The most in-depth information from Apple directly about the Secure Enclave is found in the iOS Security Guide (which is updated regularly), although this is not really geared toward consumer end users.

And of course, various Apple keynotes and patents refer to the Secure Enclave as well.

As an aside, you may find what Brian Roemmele had to say about the Secure Enclave interesting.