Usually the Vice Presidency is overrated. They are usually someone who is chosen in an attempt to get votes during the election season. Despite this they are generally well qualified and have worked in Washington for many years, but it does not seem that they actually do much in their positions. They are just a stand in, in case something happens to the President. They are also just gaining experience if they decide to run for office.
In easy times we seldom hear what the vice president is up to from day to day, so it probably seems as if he is just a place holder for the president. But that is not an easy position to be in as the vice president has to be able to take over the president's position on a minute's notice. As such, he probably has to be in on meetings constantly and be kept up to date on almost all the things the president is doing. It is possibly equally as hard to be vice president as it is to be president. The vice president doesn't have the same responsibility, but knows that he could have at any moment. It's probably rather hard to dream up things for a vice president to do in the public eye that seems very important, but the public does not see what he does on the sidelines. It's only when he is needed in an emergency that we realize what an important position he is in.
As far as I know, no one has rated the vice presidency relative to other jobs. As such, it is neither overrated nor underrated. There are debates on the powers that the vice president has, and how effective he can be, but the record of vice presidents span the spectrum of activity and influence.
The vice presidency is an extremely important position to be held. They are the second in command and will take over if the president can no longer perform their duties. The vice president is also the head of the senate, which in and of itself is a huge responsibility. It would be very difficult to overrate the vice presidency, considering all it does.