I don't think advanced civs not getting involved is a counterexample to the colonialist template. "Get involved or not" was a standard dilemma that e.g. the British Empire, or indeed the US, faced – think of the US after the 1990 Gulf War, for example, debating whether to enter Iraq and topple Saddam Hussein. Empires don't always choose to interfere, and non-interference does not mean they exert no effect on their neighbours.
One way to check whether Banks' characters are bland: look through these posts. There's a bunch of fans posting here! Lots of them talking about their favourite books. Not one mention of a favourite character. Now, imagine talking about LOTR without Frodo and Sam, or The Left Hand Of Darkness without its hero.