I'll agree that a skier, wind surfer, and hockey player may have use for unstable surfaces, because their activity is done on real or virtual unstable surfaces. I'm not sure if the OP does those activities. I don't.* A football/rugby player changing directions at full speed, off one leg, while under the influence of extrinsic force.
* A down hill skier negotiating corners as they descend from flight at over 100 km per hour to land on one ski.
* A wind surfer working to control his sailboard in inclement seas with 50 kph winds buffeting the sail.
* A hockey player bouncing off body and board while contacting the ice with a mere 1/8 inch of steel.
What I do do is play rugby and occasionally football. A much better use of my time is actually changing directions at full speed, off one leg, while under the influence of extrinsic force, rather than trying to emulate that incredibly complex set of forces with an unstable surface. For the majority of people who's sport is played on flat ground, this is the best approach.
Hockey players aren't usually that far away from ice. They shouldn't have any trouble just skating to improve their skating.
Wind surfers and skiers don't always have the opportunity to practice, so they could probably benefit from unstable surface training.