Obviously you can also invest in any of the audio/software courses (Assamil, Pimsleur, etc.) I always considered them a bit pricey and never bought them myself, and I'm not recommending them particularly, but they *are* targeted at exactly the skills you most need to build right now.
I failed the N2 and the N1 once each before I passed them.
The real key to passing the JLPT is just to do a lot of listening and reading of native materials, and to study enough to understand them.
Essays and documentaries are ideal because of the kind of material on the JLPT, but anything is better than nothing.