Running in loose beach sand?  Good luck with that.  It is hard as heck but will make your legs and feet far stronger. On the other hand, running in soft sand could raise the risk of overuse injuries due to all the stress being put on your legs.

The key to beach running is to find the packed sand and not get too wet by paying attention to the incoming waves.  Perfect running conditions, especially on a softly-sloped beach.

Surfing Vol

Beach running is great as an addition to your regular training program.  I assume you are running barefoot when you do it.  You will find that you are using alot of different muscles and in a different way which can greatly enhance your strength and resistance to injury.  Like intervals or hill repeats, I wouldnt suggest that be the only running workout that you do.  Mix it in with different surfaces and you may find that you feel stronger with a more powerful push-off.  Good luck.