Although at first glance, sending humans to Mars may seem like a waste of money, I believe there are huge benefits to be gained.
For starters, the Mars mission will necessitate the need for developing new technology which will ultimately be used on Earth for all our benefit.
An example that springs to mind, is the creation of a genetically modified wheat that is planned to be used on the Mars mission which grows extremely quickly, grows efficiently (little wastage) and is highly resistant to disease. This new form of wheat is already being developed by NASA in anticipation of a manned Mars mission. This could eventually be used to improve the food situation on Earth.
There are many more examples of the benefits of technology developed originally for use in space but my mind has died following a hard days work lol.
In addition, this will be the next big step in our exploration of our solar system and later on maybe other star systems. We have to start somewhere so it may as well be Mars.
See you on Mars!