Could public opinions get drawn in a sea of online vioces ?

It is certainly true that those with access to the internet have more influence on the framing of policy than those without. But this is only partly because of this access itself. It is also because they represent the new urban middle class which has largely developed since China's economic modernisation beginning in the 1980's. Even before the advent of the internet this class (or in the beginning the creation of such a class) was given priority.
But before this class made their voice heard it is not true to say that there was such a thing as a 'traditional' public opinion operating in China. I would rather say that there was a general absence of public opinion (apart from a fairly small administrative elite).

I think that the development of a public sphere amongst the (relatively) wealthy is a positive thing. It is certainly better than the very limited public sphere which existed previously. Of course the priority now should be to extend this public sphere to the less wealthy. This can be achieved in two ways. Firstly, by continuing the development of China in such a way that the entire population become better off (in which case more and more people will enter that 'class' which participate in a public sphere); and secondly (because the first initiative is a long term one), of finding ways to allow those who are not now wealthy to make their voices heard (a rather difficult task admittedly, and not only in China, but throughout the world).