Once you are familiar with the structure of a song, you have the basis for improvisation. How can improvisation be overrated?
If you can improvise, I´m not talking about shredding, but let´s say you are comfy enough to add your own flavor to the music you play, it´s just a way to show that you take the music/song seriously enough to really check it out.
It´s cute when kids play something difficult, but the trend of being a youtube shredder that can play a short, complex piece of music really fast just stinks...
Depends on what you mean by improvisation. I like it when a player adds his own flavor to a song. I expect it, unless I'm listening to a tribute band. OTOH I dislike unrehearsed off-the-cuff wanking. Actually, dislike is too mild a word. IMHO it's not only overrated, it's usually obnoxious. Not that it bothers me, I never listen to anything like that if I can help it and certainly don't play anything like that. Still scarred from sitting through most of a dreadful Airplane show 44 years ago.
Playing something note-for-note is a skill in itself. Creative? No, but it doesn't pretend to be.