Well, language exists to convey meaning to other people who speak that language. Did you miss the whole subplot about the linguist trying to decipher the language over the course of the show? The Japanese characters in Kuuga do not speak Grongi, and the original viewing audience did not understand it, either. If you subtitle the Grongi you will significantly alter the experience for anyone watching it for the first time. Since most people hold back on watching Kuuga simply because the available subtitle are so bad, this is going to cover a lot of people.
I don't know for sure one way or the other, but if the Japanese region DVDs come with grongi translations it's probably through optional subtitles that you can turn on and off, for people who have watched the show once and want to revisit those scenes with a new perspective. Add the grongi translations in a separate text file, if you want. But people should have an opportunity to watch those scenes the way they were originally meant to be seen.
And while I think it's a good thing to resume a series that someone else has dropped, lay off on dissing the other guy's translation, okay? Every translator makes mistakes from time to time. I could call out a few shaky bits just in your OP translation, as well.