Useful? Yes, as a reminder or way to encourage yourself (e.g., "though I am tempted to waste my money, I will be self-disciplined like my patron god") - but that's entirely apart from any mystical aspects.

I agree with this as far as rational belief is concerned, and on a denotational level. But I'm not sure whether one can achieve the very tangible benefits of enacting rituals involving such "gods" as Pan, Wodan or Hermes/Thoth without alieving that the gods are really there at some level--if only as archetypes of one's unconscious psychology--so that one can relate to them on their own terms.

As long as the "gods" are not literally considered as supernatural entities (whatever that might mean) believing in them needs not be any more irrational than believing in any other features of our psychology. But successfully channeling a god might require us to connote that belief in ways that will seem quite foreign to a rationalistic, logically-oriented mental stance.