Do A+ grades (as an undergrad) matter at all for graduate school?
If your undergrad school awards more GPA points for A+ rather than As then you should definitely try to get A+. As a matter of fact, you should always be trying to do your very best anyways. But for a top program this will be especially important. If you go to grad school, academia will be your full time 9-5 Mon-Sat job, so I would say go on and start early. treat your subjects that way in undergrad and excel in every way possible so as to get into the very best program possible.