Actually, having talked to multiple people who know Japanese about this, one of which used to be a professional translator for a good while, translating Nagoya-teenager dialect as Valley Girl dialect not only works well, but in fact scarily well.
Reading through level 1 and level 2 spellcards, I can assure you she doesn't speak in a Nagoya-teenager dialect, or any unique regional dialect for that matter. If you were to forcibly put a dialect on this, it would be Tokyo-Kanagawa dialect (which originates to Toka dialect). In fact, Japanese people may often react to the phrase ending じゃん with "Oh you must be from Tokyo."
I, as a Japanese person who has been to Nagoya and knows many regional dialects and what not, must say that Valley Girl as I know it would not be a substitute for Nagoya dialect. However, if, by the term Nagoya"-teenager" dialect, you mean something related to ギャル語, then yeah I guess so. However again, Valley Girl makes a good substitute for any light-to-heavy ギャル語 regardless of what region of Japan it comes from.
Reading through level 1 and level 2 spellcards, yes, some parts of the text have some スイーツ(笑) to light ギャル語 type of text. Therefore, some ", like"s and "totally"s are in order.
However, putting up a few examples, I don't think these are good uses of this translational method imo.
記事のネタが欲しかったから協力して貰おうかなー。 Maybe I'll just, like, take one to give myself some more material.
実際にネタを集めに出ようと思うの I think I'll, like, go out to gather material.
文こそ息が上がってきたんじゃないの? Don't you, like, need to catch your breath yourself?
etc. I find many more to be needless in terms of accurate translation. It's not really about the literal translation I'm concerned about. More so the level of annoyance I feel from the original versus the translation. Holding up a character's image is based not so much on the translated text, but more so on how the text is recited in the reader's mind. Therefore, I don't believe that the ", likes" and "totallys" that don't appear in the given text in anyway is necessary.
If translators think かなー, 思うの, and こそ→の? or whatever else they found in the text or its surroundings is enough to add that ", like" in the very few examples I put up, I would go tell them to imagine they're translating lines by Kagami or Tsukasa from Lucky Star (characters who speak the same kind of text (same words, same dialect) but with completely different tonalities and feels). Yeah, they're not Hatate, but if they were good translators, they would know what I mean (too hard to explain in words).
Aw man, half of me really regrets jumping in on this thread.