Raising it to 4 mana makes the Echo keyword kind of pointless, restricting it to only being played 2 times in a turn, unless you play Snip-Snap in a deck that does run mana discounts, such as Reckless Experimenter or Summoning Portal.
Personally I would remove the Deathrattle in the first place, and just make it a 3 Mana 3/3 with Magnetic and Echo, basically make it a Magnetic Walnut Sprite.