I don't think long term stuff like this is usually worth it. Clam spamming is also incredibly boring and is the kind of stuff that makes people just quit the game and say 'fine you win' if you actually pull it off. Not something I'd ever feel like doing.
1 clam a turn would break even a lot sooner than 50ish turns. After 10 turns you'd have produced 55 pearls, which covers the cost of the empowerment. And each clam covers its own cost fairly quickly.
I reckon after 25 turns you've probably pretty much covered your costs, and you're raking in a fortune from then on.