Is the Approach S72 worth upgrading to from the S70?

On the 47mm, the screen and battery are identical, so the upgrade adds the Elevate Gen 5 sensor with an ECG app, a titanium-and-sapphire case, wrist-measured swing metrics, green reading, and off-course maps. An S70 owner who is happy with the round itself gains the least.

Do the Approach S72 swing metrics need club sensors?

No. Hand speed, backswing length, wrist rotation and swing plane are measured from the wrist. Approach CT1 and CT10 sensors still add automatic club tracking.