Notice: I deeply apologize if I'm missing a Logical Issue to this Plan.
Instead of ending Juno's mission in 2018 by deorbiting it into Jupiter why not follow these steps.
Allow the amount of time the Scientists for Juno want to spend studying Jupiter be used. (Until Feb 2018)
Juno enters mars orbit.
How Juno is already prepared for such a mission:
The area of Juno's solar arrays will be able to easily power itself, its solar arrays are much larger than any mission before.
2: Mars is much closer to the Sun then Jupiter is so Juno will get a giant increase in power, 8x more.
Benefits that will come from such a mission:
Nasa raises interest to the General Public and proves that they are ready to get moving on the mission to Mars.
2.Juno could be used as an additional communications relay satellite for Opportunity and Curiosity along with future missions.