"The plane ticket to Italy is too expensive!"
I think it is needed because of the use of 太, rather than for emphasis.
I actually think 去 is necessary. Without it, you could just be saying that plane tickets in Italy are expensive. In this case, 去意大利的 functions as a prepositional phrase, not a verb-object combination. Chinese does not have a preposition equivalent to "to," so often using 去 [place] [的] is the functional equivalent.