Classical guitars and violins are two very different beasts in their construction, especially in the way they are braced. A violin also has a post under the bridge that gives support to the downward tension the strings impart. Steel string guitars and classical guitars are also different in construction as well where essentially the tension of the strings is braced whereas in a classical guitar the tension is merely transferred onto the sound top.
Julian Bream certainly maintains that a classical guitar loses its sparkle after a few years but perhaps that has more to do with the amount of practice a professional player does. There must also be the possibility that the guitar "dries out" over the years and becomes less flexible and therefore loses resonance.
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