I have been developing for a very long time, I started writing code in Visual Basic 5 before .Net was a thing. I knew one language basically VB, I had learned Basic about 10 years before in High School and thought how great it was to start writing programs for Windows. It was awesome, I could make utilities to do a lot of different things. I had no idea that I was in a very small club of developers, those that were using VB, everyone else was writing C++ or Visual C++ and they were able to write some awesome stuff, compared to my little cheesy stuff, you could only write games and the like in one of those C variants, which I only knew existed.
Using these languages when I could have just as easily stayed a VB/ASP.Net developer has allowed me to become a much more valuable member on the development team and to become very important to the team, which is never a bad thing. I believe it also will have made me more marketable although I am still a little scared to try to get a C# job and I am also a little scared to try a PHP job as well. The only other thing I wish I would have learned as a young developer is graphic design, not to become a designer but just so I could make my apps or webpages look better and more marketable. I highly recommend young developers to learn as much as they can and to maybe start with a C language, which will make it easier to pick up other languages. Those devs should probably also try to learn some design stuff as well, that is almost a requirement now. Broaden your language horizons so that you may be much more marketable and this will definitely help you in the long run.
Later for now.