We did a north shore exploration a few weeks ago when we were there. Traffic was not a problem at all as it was the opposite direction away from Honolulu. We stopped at Turtle Beach (saw one turtle swimming....got better/closer to the turtles at the "secret" beach on the other side of the JW) and went to Waimea Valley. There is a fee to get into Waimea but at the end of the botanical gardens walk is a waterfall that you can swim up to. It was a lot of fun.
We had hoped to hit a beach on the North Shore but by the time we were done with Waimea it was afternoon and the parking was terrible. We went back through Haleiwa hoping to hit up a shrimp truck but again the places were all swamped. We ended up eating at a Mexican place in a small plaza which was actually pretty good.
Some of our party stopped at the Dole plantation on the way back but we did not.
There is definitely enough to do on the North side to make a full day of it.
Jim