Conclusion: If you're doing the Spirit Tamer quest, grind on it. I got about 8 of my pets leveled up (this was before I was in possession of my new stylish Safari Hat) which really helped me get the Singing Cricket. Take a bunch of bandages, and stand there until you've left a groove in that spot. Pick your favorite, do it over and over, save Thundering for last because he's a flatulating turdburglar.
Nah. It's not worth it. Just finish the quest. Each of those spirits become a trainer in their own right however, they give you shards and valor, plus spirit pet supplies. You need to defeat them so that you can get the fabled quest. When you defeated the fabled quest, you open those three dailies which give you around one lesser pet charm (25% more pet exp for an hour) each.
You can easily level a good four to six in less than an hour with all those dailies plus you get a whole ton of all the rest (money, pets from the bags, etc.) I think initially it seems awesome to do it like this but I think you come out ahead by going the daily route.
Thundering, btw, is easy with an s/s rabbit and son of animus. You can easily put a carry pet on that battle.