It's well known that some things are better left in the hands of the authority.
In Business Management you learn different Management Styles - The one you are referring too is a Consultative style. The greater disadvantage of this, which drastically affects MassiveCraft is how "time consuming" it is. The behind the scene work all the Mods do and all the grand projects they create are done in a limited amount of time for the public to see. Asking them to base whether they should implement them based on a population which is (guessed estimate) at least 70% less then 18 years old, is time consuming and a set up for disaster because young people such as ourselves don't usually put a lot of thought before voting on something (possibly one reason we don't get votes in elections).
Besides this, the public doesn't always know what they want. I think we can all say that, from experience, we sometimes judge things by the cover, before we see it. However, once we have read the content, we really begin to see the advantages of it.
If you've been on the Forums for a while, or actively checking, you will see MonMarty actually does ask the public on a few things every so often, and the administrators have also offered a sub-topic in the forums that allows you to put forward your ideas/suggestions, which gives us the opportunity to show a idea to the community or discuss someone elses.
Overall I think the idea of the poll is unnecessary, and a possible shot for disaster.
Nice thought though.