Dumb question..but just wondering ?????

Considering the thinness of the wood veneer on most speakers, I would doubt it would have any effect on sound as it aged. However, those few speakers with solid wood enclosures (as opposed to mdf or synthetic ones) most certainly should age, in theory. Interesting question...

Cherry does oxidize or darken with age.

I agree w/Rcprince about veneers and wood. Perhaps the question should be "what happens to MDF over time in terms of sound"

In my case although I have kept speakers for long periods of time I have always tweaked some part of the system so can't properly asses the issue. I am really curious to hear what others have to say though.

Prpixel is almost correct - cherry does darken over time - but it is photoreactive and therefore it is light, not age, which causes the color change.

As stated above, if your speakers are veneered then it is unlikely that the veneer would contribute to the 'sound' of the cabinets. If there were any solid hardwood panels then they may change over time, but I would suspect that the change would not be positive. If I remember correctly, the body of a string instrument is intended to resonate and, as such, contributes to the sound of the instrument. In the case of a loudspeaker, I don't think that the cabinet is supposed to 'participate' in the same fashion.

Perhaps more knowledgeable individuals will chime in.