The one time in my career that I worked with management consultants, I wasn't all that impressed. The partner and one of the associates were sharp enough. The other associate was not.
That said, they created a big fancy spreadsheet that kept the business planning people happy and basically validated what we had been telling senior management.
I'm not sure that's bad though. Having been, at a later time, an IT industry analyst myself, there's certainly some value to someone coming in with a fresh set of eyes, without the biases and mindset of people within the company, and (as you say) without the motivations to push a project that may not make sense.
