It is really crazy how some problems never seem to be fixed. Some problems that were issues 50 years ago are still problems today. Some authors are trend setters and are a bit ahead of their time. Sometimes it takes 50 years for everyone else to catch up to where the author's mindset was at, like in the book, "The Elements of Style."
Language changes with the times. This is an irrefutable truth. We can even see that in recent years, when words like "selfie" have been added to the dictionary, and people have begun including completely contradictory definitions for words like "literally". However, English writing style needs a solid baseline -- an underlying foundation upon which new forms can be based. In that regard, while some things may have changed, The Elements of Style still strikes at the heart of proper English writing, and in that case it is still indispensable today.
I think that the book The Elements of Style is still indispensable even after being in print for 50 years. I think that while some of the phrases and information in the book is a bit outdated, I think there is still a lot of material in it that can be useful for a lot of people and situations today.
If one was to read though The Element of Style, one would see how indispensable it actually is. In a lot of ways, I think it is even more valuable now than it was 50 years ago. There is a certain conciseness and eloquence about it that is unmatched elsewhere.
The unfortunate side of all things in print is that they are all dispensable. There are some people that hold on to the value of paper, but they are a dying breed. Most magazines or newspapers have seen a huge reduction in sales due to the internet. "The elements of style" is likely to share the same fate. People just aren't reading paper anymore. Move to a website or perish.