I think a varied diet is more important than enrichment. Much of the food available for seahorses comes from freshwater sources, which has the wrong type of HUFA's which can lead to fatty liver disease.
If you can get them to eat other food sources, that would be idea. For instance, H. erectus is pretty good at taken anything you give them, so cutting up squid, shrimp, etc . . . would help vary their diet. Hikari "plankton" is actually small krill, another good source of the correct HUFA's. However they have a hard shell so some seahorses don't take to it.
You can also enrich live brine shrimp a couple times a week if all else false. I like Algamac, but you have to buy it in pretty large quantities. Super Selco is also a good choice if you can get your hands on it.