Writing the dissertation usually implies reusing the results you have already published or tried to publish. In this respect, you have a solid basis for writing and your supervisor becomes, as Choppy stated, your peer-reviewer. However, the supervisor should say what is OK and what should be changed, his role is rather to help than to criticize.
Regarding reading other dissertations - you are almost surely supposed to do that. You should inspire how to write, how to structure, what should the dissertation contain, how to begin and how to conclude.
Your tone, however, resembles me the situation in our department. There are many procrastinating people, many almost-active ones do not learn new things and rather forget what they have learnt. A few very active and smart people are either very busy or so single-approach oriented, that it is even hard to consult with them. This severely demotivates new students. My office-mate works on his research 2 years longer than me and he still does not have graduated. What helped me was to look at the "stars" of the science, read book from Halmos, papers like "A mathematician's survival guide" (here: http://www.math.missouri.edu/~pete/p...ch/140.MAA.pdf
) etc., and just try to do my best just for myself, to improve my status, rather than look at others and compare to them. This way of thinking keeps me in motion, in learning new things.