I've used the techniques described here for as long as I can remember (over 30 years: man, how the years have passed!) and here's how I'd summarize my experience:
1) The techniques work well to impress your friends and family (you look like a genius weaving that magic) but better still, they work wonders for examinations that require lots of memorization (think history, biology, geography, chemistry, literature and so on.) In a world where we all agree memorization is not the best way to go, our education system can't seem to avoid it. These memory techniques help you to "tape" the facts and spit them out appropriately - no thinking, no stress. They've allowed me to get done with the memorization quickly, and move on to where logic and analysis is actually required. A double win.
2) The other great fear in life - public speaking - is also neatly handled. Among other things public speaking combines the recalling of the content of a story, and the presentation of that story. We fear we will forget on the one hand, and that we will screw up delivery on the other. These memorization techniques make the recalling a breeze, and allow you to focus on the presentation. Worth it's weight in gold.
3) Finally, on the questioning of the value of the "junk associations" connected with these techniques. As others have pointed out, the reality is our human mind creates mostly junk associations anyway. We remember what we remember only because those mostly junk associations are vivid. These memory techniques teach you how to make vivid whatever junk association you use via heightened or over exaggerated imagery.
What I've found is that while the short-term benefit is better short-term memory, in the long-term the exercise of such vivid imagery has made me much more creative in the way I see things. Sometimes crazy but mostly creative, and lots of non sequiturs that bring out a crazy sense of humor that keeps you chuckling along to better ideas.