Sometimes, one of the most instructive exercises for those of us who review top-end sports and luxury automobiles is experiencing a marque’s more modest offerings. And the new Audi A3 Cabriolet and S3 Sedan speak volumes about how the German manufacturer treats its entry-level customers.

We recently took the all-new 2015 A3 Cabriolet 1.8T FWD S tronic (quite a mouthful) for a quick jaunt to Rancho Valencia Resort & Spa in Rancho Santa Fe, Calif., about 135 miles from Los Angeles. Equipped with a 1.8-lit…