Indeed structured data in webmaster tools shows errors, but that doesnt mean that Google will put the stars up. If you want to more easily browse your site search results for stars, you can tweak the search settings to display 100 and include duplicates. This wont answer your question directly, but will give you an avenue to see what is activated in indexed pages.
Step 1) Go to google.com and click the "gear" in the top right corner. In the dropdown, click "search settings". Under Google instant predictions click "never show instant results". Now, move the slider for "results per page" all the way to 100.
Step 2) Go back to the google homepage and search for your site by using this query:
site:www.mysite.com. Press enter and you will see X amount of pages of 100 results. Paginate through them all the way to the last page and you will see something like:
repeat the search with the omitted results included. Click that and now you will have a list of everything.
Step 3) Manually record the pages urls that have stars activated. Hit up analytics or whatever and look up that page/bounce/funnel/etc. This should give at least some kinda very raw overview and since you recorded the urls you can keep track of them in the future.
Step 4) Reverse steps from step 1 to make your google act how it should (turn instant back on, set per-page back to default). When you wanna check again weeks later, start from step 1. If you find yourself doing this often, you can make a test account on google and use Canary branch of chrome (or as an alt signin user on your normal chrome).
Bonus: Remember that serp widgets change based on your Google+ logged in status. stars may appear for you when they dont for non-G+ users or vice versa. Try the test both ways to get a good feel for the schemascape.