Lithuanian is mostly phonetic. And "mostly" here is just a precaution to take some edge cases into account. Some diacritics just modify the length of the base sound (Ą, Ę, Į, Ų, Ū). I would not say that case Ė, Č, Š and Ž warrant having a completely new alphabet. If that was a case pretty much any language that has Latin-based alphabet should get a new one, because pretty much all of them have their own additions.