I've owned both.

I still own the 324s.

The 530s look better and are a touch lighter. Neither of which is a concern for my 35lb touring bike. The platform of the 530s gets slicker than owl snot with a drop of water.

The "cage" of the 324s provide a much better grip in bad weather and have eliminated the "hot spot" under the ball of my foot on the SPD side that started at 30-35 miles with the 530s.

I got a pair of Wellgo WAM DA10 SPD/platforms that I haven't mounted yet to try.