DEFINITELY worth it at the current prices. With a length-of-stay, it's nice to be able to spend 15-20 minutes on each of several days, instead of worrying about "getting your money's worth" on one day.
BONUS: Once you've gotten your daily "punch" on your wristband for Rainbow Reef, you can also use snorkel gear from Makiki Joe's on the beach. We'd brought our own masks & snorkels from home for use in the lagoon, but learned this tidbit on our last day... next time, we'll save that space & weight!
BTW, snorkeling along the breakers in the lagoon is OK - on windy days the water will be stirred up, but you do see many species of fish in their "natural" habitat. We even saw a Green Turtle resting on the bottom - there are none of those in Rainbow Reef!