Unless your truly need the money, or never travel....keep the the backup!
Lenses are tough, they are made with the thought that they will receive a certain amount of abuse... However, remember Murphy's law, If it can go wrong it will, and at the most inopportune time.
Case in point, last spring I was in South American my favorite walk around zoom died. I was just sitting there snapping off a few shots and all of the sudden the barrel went loose. Had to spend the next two weeks, using either the cheap little kit lens or the 100-400.
After returning to the states, I bought a new (and nicer lens) and sent the broken one back to Canon for repair. Cost was $175 to replace the barrel.
A couple of weeks later, I went in Hawaii. On the way back home TSA dropped my body & the 100-400. They fell 3 feet, onto concrete and bounced!!!! End of trip, had back-up.... nothing broke.
As a general rule, I didn't and don't worry too much about equipment failure.... on the other hand why tempt Murphy?
Since I travel a lot, it was worth paying the $175 just for the piece of mind that I have a decent back up.