It wouldn't be worth it since I can catch Magikarp at this one library near me and I usually go there once a week.
Plus I'm already in the middle of getting candies for my Grovyle. It had 30 candies to begin with and after walking
with it for about a month or so, I have 61 candies.
I'm only 11 candies away from being able to evolve Magikarp and I'll probably use some of my rare candies once I reach 398.
Yesterday I evolved Weepinbell into Victreebel and Koffing into Weezing. Today I caught my first Nidoking and I decided to evolve my Mankey into Primeape.
I was originally going to wait until it had more candies but it had such low cp (only 400) that it wasn't worth it. My Primeape is only cp860.