As someone who's been in the exact same situation as the OP, I'd disagree. Rosetta is quite good if you want to acquire new vocabulary, but if you want to brush up on a language you used to know quite well, Rosetta (or any software) is quite useless. I've found that the ONLY thing that actually works is taking conversation/refresher classes. I'm very happy with the options at my university.

In the case of total beginners, Rosetta works quite well, but my SO, who has been a reluctant student of German for a year or so, is just as happy with the language software sold at Costco. So I'm not so sure if Rosetta is worth the money.