Some are easy calls -- almost all music theory today points back to BMW 846-893 for example.
Right - the BMW 846-893 series was produced in Leipzig in the 1730s, and was famous for its innovative style combined with meticulous attention to detail. The sound of the motor was legendary ("Well-tempered"), whether one was slowly cruising the back streets of Leipzig looking for errant choirboys, or racing down the 18th century autobahn to try out the new organ in Weimar.
Bach was so impressed with the series that he made sure to compose his 48 preludes and fugues at exactly the right time so that they could later be classified as BWV (Bach-Werke-Verzeichnis) 846-893, a fitting tribute to those magnificent automobiles which he had so loved.
I don't know -- if a composer's influence doesn't extend outside of his genre, is he really that influential?
Some are easy calls -- almost all music theory today points back to BMW 846-893 for example.
Others are tougher, Haydn basically invented the modern symphony, but his own compositions aren't widely considered particularly original in terms of the symphonic tradition as a whole.
Few students of classical music would have spent much time with Purcell and the English school of Baroque music, as another example, but almost all of Rock music and a great deal of modern Jazz is influenced by Purcell thanks to The Who being big fans.