Yeah, there's a bit of a vicious cycle. We need to understand grammar to read books, but we need to read books to practice our grammar. 
For me, the longer the sentence, the more trouble I seem to have. Suddenly I'm surrounded by a sea of particles -- or, worse, particles have been omitted (as in manga), and I'm really at sea. Or I have trouble figuring out where one word stops and the next begins. In fact, if I had one wish for Japanese script, it might not be furigana -- it might be spacing of words. (Again, manga helps with this somewhat, as line breaks are frequent. And of course a better vocab would help the most.)
Anyway, I'm wondering what grammar tool I should study next. I've read Japanese the Manga Way (and re-read much of it); Tae Kim; all of Genki 1/2; half of Hosogawa's text; and most of the Dictionary of Basic Grammar. I suppose the Dictionary of Intermediate Grammar?

For me, the longer the sentence, the more trouble I seem to have. Suddenly I'm surrounded by a sea of particles -- or, worse, particles have been omitted (as in manga), and I'm really at sea. Or I have trouble figuring out where one word stops and the next begins. In fact, if I had one wish for Japanese script, it might not be furigana -- it might be spacing of words. (Again, manga helps with this somewhat, as line breaks are frequent. And of course a better vocab would help the most.)
Anyway, I'm wondering what grammar tool I should study next. I've read Japanese the Manga Way (and re-read much of it); Tae Kim; all of Genki 1/2; half of Hosogawa's text; and most of the Dictionary of Basic Grammar. I suppose the Dictionary of Intermediate Grammar?

I honestly had no idea about a lot of the linguistic concepts in the introduction, especially the logic behind the sounds used for 擬声語 and 擬態語 and by extension the reasoning behind many sounds in the language itself.