Pollux: Keep in mind that when I refer to "extra" features, I'm talking about two things:
1) The silver-gilt edging. If the current edition has this edging (which, at a 15 US$ price, I would tend to doubt, but I can't say for certain because I haven't seen the current edition), then the AGM edition wouldn't be "special" in this regard.
2) The Epilepsy music CD. The earliest edition of the AGM version did not
include the CD. The first edition was packaged in a silver/gray box. The later edition, which included the CD, was packaged in an aqua/blue-green box. In any case, keep in mind that just because you may be purchasing the AGM edition, it does not
necessarily mean you're getting the CD. Which isn't necessarily a problem -- just make sure that you aren't expecting to get it for the price you're paying unless you've confirmed that the CD is included.
First editions that come from different publishers than later editions, or that have substantial differences in printing, packaging, etc., are always more valuable on the collector's market than later editions. However, the existence of later editions almost always does bring down the overall value of early editions, even if not to the level of the later editions themselves.
Again, 40 US$ was the original price of the non-CD edition that was distributed in the U.S.
Hope this helps.