I didn't use minna no nihongo (I was too GENKI), but once you've cleared the intermediate learning materials, there are a lot of materials you can use to improve your Japanese. I have a box of various textbooks and back home, the only ones I remember fondly are "
Cultural Episodes" by Japan Times (a series of increasingly challenging essays, the cover in the link is different from the edition I have but from the reviews I think it's the same book),
日本人の知らない日本語 (super interesting and great reading practice) and
How to Sound Intelligent in Japanese, which I obviously never finished reading (HAH self-own), but found entertaining because it mostly talked about the theories of Japanese, which I enjoy.
I have some materials specific to studying and even N1 textbooks, and honestly I've never spent much time with them because I'm not a very motivated self studier. I've also never taken on any of the JLPT exams, but I've taken a few practice tests to check my level, and though I'd crush the N2 I know I'd need to seriously study to pass the N1; the difference between N2 and N1 is pretty huge. If you're really goal-oriented it's fine, but why not clear your materials first and take the N2, then gather new materials and focus on N1?
Bottom line though, JLPT is a better indicator of your ability to take a test than your language ability (though It's perhaps a bit better since they revised the test structure). Once you get comfortable in Japanese, spend some time enjoying it by reading books, watching movies, and talking to people; your language ability will develop naturally, which will make the studying easier too. Worry about the test later, nobody else really cares what "level" you are anyways.