Thanks, it is helpful to know that. We once looked into a Russian Orthodox church and the parishioners did seem to consider Russian-ness an integral part of church membership. so much so that they seemed distinctly unwelcoming to non-Russian converts. Having said that, I do believe that a strong ethnic component has enabled the Orthodox churches in the U.S. to withstand the assaults of "MTV culture" better than the Catholic and Protestant churches have done.
If we are holding the MTV culture at bay with greater success it is because of our anti-western and particularistic tendencies, rather than ethnic identity issues. My children probably don't know what MTV even is, at ages 11, 13, 15, and 17. My husband and I think we have held off "westernism" from them (so far) with success because of many parenting choices, but none have to do with ethnicity.
I'm not sure it's just the ethnic component that helps the Orthodox resist the secular culture. Some of the Orthodox who do that least well are those who wear their ethnicity on their sleave, but don't live the life of the Church fully.
The thing that makes it easier for the Orthodox to resist secularism is the fact that Orthodoxy offers a comprehensive way of life rather than just sound doctrine and a way of worship.
In terms of openness to converts, I think on average we Antiochians are the most open, followed by the OCA, but mostly it varies community by community (some ROCOR parishes are very Russian, others are mostly convert). I'm told in Western Europe, the Serbs are the most open to converts, and sometimes one finds that here, too. (Kansas City, has a majority African-American Serbian Orthodox parish, St. Mary of Egypt. (!!!) And a young man whose first contact with Orthodoxy was a visit to our little Antiochian mission later converted at a Serbian parish and entered seminary--I've not heard whether he's finished and been ordained.)