Slim I agree JWs have had a disproportionate cultural impact, given their numbers.
I put that down to a couple of things. It's an American, English speaking religion, which helps the spread of information. That info is ubiquitous and free of charge, with a very recognisable artistic presentation and engaging concepts story wise - Armageddon, paradise etc etc*
Also witnesses themselves impart their culture to the wider world. Because of the way witness kids are raised - with an abundance of boredom - they learn the ability to entertain themselves. The few outlets they have, for example music (ie learning the piano), they attack with gusto & real appreciation. Witness kids are forced to be responsible and disciplined - thus there are a more than average number who excel in the arts, music, business and to a lesser degree sports etc
*And preaching, of course. Most people have a neighbour or friend they've met through the work.