I've never read the high fantasy novel Lord of the Rings, though I've seen the movies a few times.  Do you think it's worth it for me to read them?
I think it is! They are very popular. So many people love them. 
Is the writing at all similar to the Hobbit, the classic children's book?
I think it would be very similar but I cannot say for sure. It is very long, though so you will want to commit to it. If you really liked the movie, I think it will be worthwhile. 
It's probably worth it, since so many people like it.  I know it's sold over 150 million copies, so it must be good :P
That is mind-boggling when you think of it - that so many people have read it. But it is definitely a good endorsement! 
The only way it could reach more people is if a celebrity decided to endorse it or put their branding on it :P  Thankfully that'll never happen.
No, I think it does well enough on its own. Sometimes it is just nice to read something that so many other people like so that you feel like you are informed and understand it. It would also make the movies more enjoyable, I would think. 
I think one thing that makes it so popular is how the story goes from quiet beginnings to a full scale War by the end of the books.
People like those really epic novels that have rich characters and a lot of action. There is a lot of story behind it, too. People have been reading it for so many years.