I think the real value of taking an etymological approach will be found in how a select few of ESL/EFL students will pick up the ball and run with it.It's definitely not something I could spend a lot of time on, considering time constraints coupled with curriculum demands; albeit, there will always be a few students whose interests will be piqued enough to add it to their own mental tool box.
I think your suggestion to do a comparative study to determine its value is a good one though. I'll definitely give that some more thought.
I think too that it's interesting how so many students have learned the International Phonetic Alphabet and actually apply it to their learning. (Even though I once learned it myself, I've never felt compelled to use it in any of my classes, be they ESL or EFL classes.) My meaning is that since they have the motivation to learn the IPA,then what would prevent them from doing further linguistic research in terms of etymology? I guess the answer is fairly obvious and it gets back to what we've touched on here before and what Yingwen recently mentioned about students needing to take the responsibility of learning the language into their own hands; moreover, they need to realize or be made to understand that we are, after all is said and done, only their guides.

Those students who have responded the most positively to my lessons on word roots etc. fall into two categories now that I think about it. Those in the first category include those who naturally crave knowledge and can determine for themselves the value of any additional information that will pave the way toward that knowledge. The second category includes those who simply want an easier path. Maybe I should add a third category - those who are tired of the same ol' song and dance and simply want a way out of the doldrums. In that regard, I had to negotiate with our leader in terms of how much reliance I had to place on the text book provided for my classes. He started out at 70% and I at 40%. We finally agreed on 60/40 and later he accepted that the book should just be foundational. Fortunately, we'll have a new text book this coming term. The old one was the worst I've seen yet.

Just got back from the dentist. I think it's pretty cool how the Chinese doctors and dentists - not the quacks, but the real ones - are so much more communicative, kind and open than their counterparts in the West. Guess it's because they don't have one eye on the clock and the other on their bank book.