I've never thought of El Cielo as being accessible by any means other than boat or helicopter. There is literally nothing at all there, so if you found a tourist trap you were not there. It's my single favorite spot on earth, and I spend my daughter's birthday and the anniversary of her death there every year. It's good for sea stars, conch, juvenile angelfish and, I suppose, turtle grass if you're a big fan of that. We've seen turtles and sharks (between us and the beach when we were only knee-deep). It's not a place to find coral or large fish. It's just a really nice, beautiful beach. In the many times we've been, we've never seen another soul there.
You might be thinking of Punta Sur, which does involve a fairly long dirt road. If you hike north along the beach from the farthest you can drive, you eventually hit El Cielo. The road is sometimes pretty bad, sometimes great. We have no difficulty managing it in our little Nissan Note. I sort of like Punta Sur for a beach day now and then. There are some vendors (snorkel gear rental), some loungers, and a shack where you can buy tacos and beer, but I really wouldn't call it a "major tourist trap" by any stretch. It's always seemed pretty sleepy to me.
Are you sure this was Cozumel? cicopo already pointed out that there is no Gulf side. At its nearest, the Gulf of Mexico is about 80 miles from Cozumel.
I have never tried snorkeling on the east side of the island. You are correct that there's not much worth seeing that would make it worth risking the currents. One goes for the beach and to splash around. Water temperatures always seem pretty much the same everywhere around the island.
I might be misunderstanding what you're saying. Dead coral is usually stark white, isn't it?
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