Add up/down voting to comments, and use the scores generated by these votes to sort and thread the comments (i.e. similar to the system employed on reddit.com). 

This platform's biggest strength is the large number of "opinions" (ratings) from different people which it can accept and summarise for each idea (as an average rating). In my opinion the easiest way to improve the usefulness of the platform is to expand voting to cover comments on the ideas as well.

Say I submit a popular idea that gets 1,000 comments from different people - that's 1,000 people who have expressed thoughts on my idea - and for each individual there's a chance that their comment tells me about a potential problem with my idea, or a way in which my idea could be improved.

Unfortunately it would take a very long time to read each of those comments and form an independent judgement of whether the commenter has a point or not. If the comments are arranged chronologically I'll read maybe the first 20/50/100 and might spot any pearls of wisdom in that sub-set. If I'm lucky enough that the best comments were also early comments then I may well spot them, the problem then is that not many other people who are interested in my original idea will have seen the same replies, and so even when good comments are spotted they do not form the basis of further discussion. 

If you allow "the crowd" to rate each other's comments you will find that the best comments (as defined by the group) tend to rise to the top where everyone who reads the idea will see them. This is where threading comes in; if you allow people to reply to specific comments then the highly-rated comments will generate their own discussions. The same principles of rating and sorting can be applied at all levels of the thread. The discussions which happen using this kind of system will tell you in a lot more detail (than a 1-5 rating) about what the people who have rated an idea think of it - and more importantly how they think it could be improved.

I know very little about the technical side of web development so I can't tell you how to handle all of this rating and sorting efficiently... in my opinion though reddit.com does a pretty good job of this already, and as its open source you may be able to learn something about it from their code. I happen to believe the commenting system is absolutely key to reddit's success, and also that its even more important to a website about ideas (such as your freedom).

Crowd-sourcing of ideas should just be the first step on this road, and it has been done plenty of times already in different ways and for different purposes... the next big advance in this area will come from enabling the crowd to not just pick the best ideas of its members but to actually improve and refine these as a group.