Standard English - Important or Not?

This week I'm responding to Trudgill's "Standard English - What it Isn't." Before reading the article I wasn't entirely sure what Standard English referred to. After reading the article, I wasn't sure if my understanding was more clear or more hazy. Trudgill defined Standard English by defining what it isn't, and then came to the conclusion that Standard English is a dialect without a geographical base (which is generally not the case of dialects).
My understanding was that Standard English is a grammatical version of English that is used in various contexts such as in novels or newspapers. I also understood that Standard English has more to do with writing than with speaking. When is the line drawn between what is Standard English and what is not? I'm guilty of saying "I don't want any," which Trudgill pointed out was not Standard English because of the double negative. If I don't speak Standard English, what am I speaking?
One of the interesting thoughts raised in class was whether the English language will become Americanized or whether it will break off and dessimate into smaller dialects worldwide. I tend to think the Americanization of English is more likely than the dessimation of the English language. When we are constantly exposed to advertisements, TV shows, movies, and other forms of pop culture and media on a daily basis, isn't it inevitable that one dominant form of English will take over others? The media influences people in every other way, so why wouldn't language have the same effect? Language keeps the world rich and diverse. I often wonder (and wondered even before this class) whether the entire world will end up speaking English one day, thousands of years from now.
 My sister is an Anglophone who pursued French in university and obtained her Master's Degree in French Literature. She said French and English are different in the sense that in English, new words are constantly being added to our language. In French, there are more strict guidelines on what is acceptable to add to the language. She said it isn't common for words to be added to the French dictionary. Does that mean French speakers are more concerned about the "Standard" part of their language? And if so, why?
It concerns me to think of grammar rules changing, words being added or taken away from the English dictionary, and younger generations having poor writing skills as a result of massive technology change. I also wonder, however, why it bothers me so much. Is proper English, spelling and grammar an elitist concern? Why do grammatical errors bother me so much when many people fail to even learn correct usage? What will become of language and writing within the next century or two? I will never know the answer to some of my questions, but I know that whenver I send a text or an e-mail I make sure to be as proper as possible. :)