The way I look at a GUI is that it is built entirely on terminal functions. I see you disagree, but I don't know how a GUI could be created without being built on something at a lower level. Something has to cause it to work, somewhere between bits and hardware, and the screen. Double click to open file? Same as `open file`. Find and replace in a text editor? Same as sed or `s//`.
A GUI can make it easier to do those things, but not always. For example I find using git in a GUI to be a worse experience than it's command line counterpart. I'm more at home with `git diff` than whatever built in attempt at improvement is available. I'd rather edit and resolve conflicts in vim than a visual editor (even XCode which is a pretty nice diff tool).
In short I just don't see myself ever moving off of terminal, and I would never see knowledge of it as a handicap. On the contrary, I'm always looking to learn how to do something new and powerful in it.