This is a great topic of discussion, thanks for starting it BB.
I have sat with rapt attention at a performance by a highly respected traditional performer who did not utter a word during the whole performance. It was brilliant.
I have also sat with rapt attention at a performance by a highly respected performer who told so many long involved stories that she only sang about four songs in each set. It was brilliant.
So to me the issue is not how much time you take introducing a song, or whether or not you say anything in between songs, the issue is that as an audience member I have to "buy in" on the journey you are taking me on. In both of the above cases, I bought in big time, because of the strength of their performance -- not just which songs, but how they were presented, what order they came in, what was said before and after, etc. In other words, they had thought about the performance almost like a theatre piece (whether or not it was completely scripted). They knew what atmosphere and emotion they were trying to create, and everything they did on stage pointed toward that goal.
One of the best pieces of advice I ever got about performing is that your task in developing your performance style is to uncover or discover who you are on stage. And who you are on stage, just like who you are in life, is going to be different from anyone else. Just like those two performers were so different, yet both so compelling.
When I'm putting together a set list or thinking about a performance, I'm always thinking about the arc of the performance. I want to have some highs and lows, some places where I talk, and maybe some places where I don't talk at all. I try to have some variety in the styles of songs I'm singing (key, accompaniment style, happy/sad, etc.) I have introductions to songs that I've honed over time, but I try not to recite a memorized speech. I also have some songs that I can introduce with an involved story or a short sentence, which allows me to read the moment and do what I think is needed at the time.
Having said that, if you are just starting out performing, it might take some time to get comfortable with the idea of being in the moment when you are on stage. So if it helps you to have memorized introductions at first, I would say do that, but with the idea that as you get more comfortable you can move towards being more spontaneously "you" on stage.