When asking for feedback from the community, be specific. The broader your question, the more tangents it will spawn in the ensuing discussion, and the lower your signal-to-noise ratio will be.
So, instead of "here is this big huge spec, go read it and let me know what you think", take one small section of that spec at a time, and ask 2-3 pointed questions about it.
Not only will you be more likely to get high-quality feedback using this approach, but you will also hear from more voices, since many people do not have the time to dedicate to reading and digesting a large proposal.
When farming ideas, encouraging more people to speak up with honest, on-topic feedback is exactly what you want.