I feel the same way, at least through elementary levels. After that, though, I think several JLPT-focused resources also happen to be the some of the best resources for self-studying lower-intermediate Japanese on up in general, so at that point you might as well take the tests too. (Or not, but just emphasizing that at later levels of learning, the “JLPT” material also happens to be pretty good general Japanese material if you’re outside the classroom. I’d take Sou Matome or Kanzen Master over Intermediate Japanese, for example.)
But yeah, @Solista–echoing the general sentiments of this thread that it would be best to go through the elementary-level course/material of your choice first, and worry about specifically targeting JLPTs later.
If JLPTs are really on your mind for early goal-setting, if you go through an introductory book/course of self-study (like Genki, or whatever alternative calls to you), you should be ready to take N5 with a little prep/review. Same for N4 with a follow-up course (Genki II or alternative). If that appeals to you, you could always go through an elementary course, then grab a round of JLPT review material (like the しんにほんご500問 line), to check yourself before the test. Whatever material calls to you, I’d definitely recommend picking something that will give you sequential elementary grammar, and sticking with it to the end.
Even though it’s designed for classroom use, I tend to recommend Genki because it’s a complete-package introduction with a workbook you can use for self-study (I personally feel that the ability to test your own comprehension of lessons is essential for self-study), though there are definitely other options too. If you go through a book/course like that in combination with Wanikani, you’ll have a pretty potent combination of materials to ramp up Japanese learning.