Unless something has changed, I believe all requests to AQS traverse Varnish and RESTBase. This means that the RB metrics already cover all Varnish cache misses. While the Varnish hit ratios for AQS entry points are low, the most complete data will be to set up metrics based on request logs. Doing this generically is a request to Analytics in T122245.
@Nuria, is there anything else you are looking for here?