We watched the last launch (Feb) from Cocoa Beach. The PP is correct that you cannot see the launch pad from there, but you can see it streak into the sky and you can "feel" it which is pretty cool.
We had the same thought as you to make it our beach day, and see the launch. However, if you do this, LEAVE VERY EARLY!!! We left our villa (near Disney) at 9:00 and got caught in hideous traffic on the way there, not arriving till noon. We did get one of the last parking spaces (paid) on the beach, but the free ones had been gone since 9 am! I expect this time it will be even worse.
After it launched, all the people who were there were trying to leave at the same time. Traffic even worse than getting there. We opted to eat dinner in Cocoa and didn't try to leave the area until 7:30. Even then, traffic was still locked up tight. We got back around 10:00, which wasn't too bad.
As it turned out, between eating lunch, getting settled, etc, we were only "on" the beach for a couple of hours.
There was plenty of space to watch the launch (since it is a HUGE beach). And, it's a nice beach.

Just plan for traffic, be patient, and you will be fine.