Thanks for your insights. Still trying to decide whether something like this should go on my wish list ;) (see above for my potential uses).
How accurate, exactly, do you think such a device could be? Obviously it's not going to be pulling out the sort of precision of a professional spectrometer. But you mention, for example, being able to identify the signatures of herbicides and pesticides. Do you mean, for example, "This contains imidacloprid", or more like, "This contains a nicotinoid of some variety"?
How useful do you think it could be on identifying mineral species - say, distinguishing between different zeolites? Or, back to food, if given, say, a mango, to get readings of, say, water, sugar (in general, or specific sugars), fat (in general, or specific categories of fats, or specific fats), protein (in general, or specific categories of proteins, or specific common protiens... obviously it's not going to be able to pull out 5 ppb of Some-Complex-Unique-Protein), common vitamins (generally found in dozens of ppm quantity - some more, some less), minerals (likewise), etc?