The site has many good and bad questions, but many are asked by new users who just disappear after asking there questions, what will happen of the good answers written by the regular users, neither the answers are voted up nor marked as correct, even by the fellow regular users. Also there are many unanswered questions or questions abandoned by the users in the view that someone is never going to answer them, which doesn't motivate them to ask another question.
many are asked by new users who just disappear after asking there questions
I don't see your point here. This is a common problem throughout Stack Exchange. Some people take a penny, some people leave a penny, it's just the way it goes.
what will happen of the good answers written by the regular users, neither the answers are voted up
The site has many good and bad questions
If you (plural) see good content, vote it up! If some questions haven't had a large number of views, those views, and by extension, the votes, will grow over time.
If you see bad questions, leave a comment for the user to ask for clarification, and if the question really is that poor, vote to close (or flag accordingly if you have over 15 but under 500 reputation points).
Best example of a excellent beta site would be "Musical Practice and Performance /SE".
I commend the music site for answering almost all of their questions, but comparing a music site with a science site is like comparing apples and oranges. Stack Overflow has 816,518 unanswered questions as of the time that I wrote this answer. It's hard to argue that the number of unanswered questions is anything but one of many criteria on which we can rate a site.
In summary, the quality of the site lies in the hands of all of its users. Users of any reputation can suggest edits, and we have a super good track record of keeping the Suggested Edits queue clean, so there's little lag time there. Any user with 15 reputation or above can flag questions that just aren't right, so even if you can't vote to close, you still have a say in the quality of content.