In mathematics, it is common that theorems/results and problems appearing dull in one generation get revitalized and become the center of research in another one.

Sometimes conjectures that are thought to be untouchable become resolved within years.

I would like to know if there were conjectures that did not appeal to a large number of mathematicians but when they were resolved( maybe partially), the techniques used or the result itself touched upon many areas. On the other hand, are there also conjectures which were expected to have dramatic impact but upon resolution did not meet to that expectation?