Perhaps this could be used for background music rather than sound effects.

Think of it this way: you could turn on some music to read while you're reading a book. You could choose something that fits the story yourself, but it usually won't fit the passage you're reading. You can have the ereader choose it, and it likely will fit the passage.

On the distaste for sound effects though, I totally agree. Unless it is done well, it is likely to be disruptive. Unless you can track exactly where the reader is, it will probably be in the wrong place. (I suppose you can extrapolate a reader's position based upon the rate of page turns or track eye movement, but I doubt that those techniques would be reliable.)