From what I understand, longer intake runners provide more low-end torque. Adversely, shorter runners yield greater high rpm horsepower.
So I say, experiment with a huge spacer. If it does give you more low end grunt, you should definately be able to feel it.
Otherwise, I've heard no positive remarks on throttle body spacers. I've known people who used them on 5.3L and 5.7L LS-1 chevy's with no noticeable effects.