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.