It is completely safe to augment any resource with
Access-Control-Allow-Origin: * as long as the resource is not part of an intranet (behind a firewall). In other words, a URL you can fetch from a server on the internet using
curl. For your basic web site this encompasses all resources on the site. The
Access-Control-Allow-Origin header (part of CORS) tells the browser the resource can be shared.
Even if the resource includes confidential information based on cookies or HTTP authentication data in the request, including the header and sharing the resource is still safe, since the browser will make the request without any cookies or HTTP authentication data. And if the browser did make the request with cookies or HTTP authentication data, it would never share the resource because that would require an additional header,
Access-Control-Allow-Credentials, and a different value for the aforementioned header.
So go ahead and safely share your public data with other applications!