Honestly its not worth it in my opinion to spend more dust on a jolteon. Especially since you already have one maxed with Thunder.
Now if this new Jolteon is a high level and nearly capped then you may want to do it if you got a lot of dust laying around as it wouldn't cost a lot to max it.
Jolteon is just too much of a glass cannon to be in the meta which is a shame cause a meta electric would really be awesome in the meta game.