Assuming that you mean the vaporeon has water pulse, I think you should power it up. Vaporeons make good defenders, with high CP. Powering up defenders can be very useful.
If Magikarp candies are so rare for you, I'm not sure about evolving that magikarp. Do you have any other magikarp that you're considering? Also, are you planning on using the gyrardos, or are you just doing it to add to the pokedex?