I disagree with seeing these books as bleak, or indeed anything by Banks (it could be because our definitions of bleak differ, since I agree with you on the other values). The SF part is simply a setting for his strength, which is to detail and praise human character. For example, he continuously breaks the "rules of good writing" such as having dei ex machina (or more properly, dei in machina with some exceptions like The Algebraist) conclude most books but he is an example where it is done in a way that augments the story.
In most Banks stories, characters (including the Minds, for example in Excession) are put in difficult situations made believable by well structured suspension of disbelief ("great craftsmanship"). They get out of these situations using their intelligence and demonstrating courage and a well defined hierarchy of values (including appropriate self-sacrifice for something they value higher than their life). This is philosophically the opposite of Story of My Life and Ubik. Even if the ending is a downer, even if major characters suffer enormously (I'm still marked by Surface Detail years after reading it... truly harrowing), reading Banks had me walk away with my mind augmented somehow.
That being said, on the First contact/alien civilisation front I always got the feeling that Banks' aliens species are always very human, representing different facets of human nature, including the Minds. I think it is on purpose, like Asimov in most of his work he was not setting out to represent truly alien species as Charlie Stross, Peter Watts or Cixin Liu have done but writing novels about human characters and values that happened to be framed by SF.