2% eh? Big deal... right?
On average, over 7000 casts in the new Harbor pools, I have caught around 1700 fish. This amounts to an average of 24% The energy gained has been 4600, or .645 energy per cast.
Adding an additional 2% of fish catches would mean 97 more fish caught. On average, a fish is worth 2.735 energy. At this point, I would have an additional 400 or so energy if I had been using a lure.
On a per-cast basis, this is .055 extra energy per cast.
While .055 energy may not seem like a big deal, over the amount of time you fish, it will pay off... especially if you are up to 32,000 casts or so in 15 days like Yours Truly.
HOWEVER, if you do not fish often, you would be much better off purchasing the 50% energy refills.