I went to France for altogether about 3 months and can say that for me, it was extremely beneficial. However, I completely understand the concerns about communication being difficult and perhaps limiting progress. I went twice, once for two months and then again for another month, and what I noticed was that the higher your skill level when you first leave, the more you will improve.
Going overseas is of course very costly, and not a quick and easy way to improve language skills. Vocab in my opinion will undoubtedly improve, along with listening. But I found I had to push myself to engage in conversation. Grammar and writing, equally important to speaking and listening, are just as easily improved in Australia than in the actual host country.
In terms of cultural difference, this is part of the appeal of going overseas. I enjoyed getting to know a different culture, but it's true that if you may have trouble being away from home in an unfamiliar environment, you may not actually progress much with your language.
I think going overseas is a fantastic option if you have the means to, the desire to, and the knowledge that it's not automatically going to make you amazing at a language: you will have to work for it. Equally, if you are hardworking, it's not needed to get to a good level for VCE languages