Grades do not matter. Accomplishments matter. If you have no other accomplishments, grades will be the default accomplishment that you will be judged against for comparison. So really, you are in complete control of whether or not grades will matter. Of course this means applying yourself.

Likewise, your future degree has an expiration date. I would estimate about a year from walking. Your degree will start to smell if you have no accomplishments to back it up. Each year past graduation, the education section of your resume should be bumped farther down the page. Eventually, it should become a matter of whether or not you have room to include your education at all. Your education should become a trivia fact. A small talk subject before discussing what you have done.

PS: I am of the opinion that anyone completing a four-year degree with a 4.0 grade point average did not get their money's worth out of college.