I checked out Spanish by Association and I can see why you're liking it.
I was raised in a bi-lingual home and so, never experienced learning another language from scratch until I studied German and Italian (but mostly German because it's not Latin-based). I'm not sure if I ever took the time to consider how I organize language until more recently.
Anyway, I had a funny experience where I consciously realized that when I hear a word, particularly Eng/Span, I have an image, a sound (music, voice), or a feeling, etc. running through my mind. These references are tagged with words in the languages I speak and in the case of Spanish I can recall them just as easily as I can in English. These associations are what allow me to be fluent which I am less so in Italian, and even less than that in German. In Spanish the associations are on par with the English while the other are weaker. It only makes sense that finding an efficient way to tag or associate concepts would improve your ability to speak and understand another language, or anything for that matter.
Strangely enough, I recently picked up a couple of mnemonic books (Thirty Days Hath September, Every Good Boy Deserves Fudge) as a result of this feeling that I should be helping my children associate many of the concepts they've been learning so they can more easily retrieve the ideas when they need them.
and see: It's on the Tip of the Tongue by Charles Zanor WAPO March 11, 2008