I had a small crack like that in my bumper and left it alone, and 6 months later it became a much larger crack, so definitely fix it!
what I ultimately did was use some Bondo 2-part bumper repair epoxy on the inside of the bumper, with some 3M metal mesh made for body work to hold it together.
you have to take the bumper off, then clean and rough up the plastic inside to allow he epoxy to bind to the bumper.
Then I put the metal mesh on the crack and spread the two part epoxy on top.
It became solid in less than an hour. don't know about the long term, I traded in that car a few weeks later. I am hoping the metal mesh will prevent the bondo epoxy from cracking at the same place where the bumper is cracked.
Then if you want to make it look better you''ll have to fill the outside of the crack with repair paste, sand and repaint, but that is a bit more work than just the epoxy.
