Sirspeedy said
as wood ages,it tends to dry out,and can change it'e properties
Not quite. Wood (we're not talking about green wood, here) reaches an equilibrium with its environment. Furniture wood in someone's home in Seattle will have higher moisture content than the same wood in a home in Santa Fe. The wood will be equally functional and long lasting in both cases. It's when wood goes through cycles of picking up moisture and expanding and then drying out and shrinking, because it lives in a climate with widely varying weather conditions, that one gets problems. Preventing the wood from being subjected to this cycle is one of the main purposes of a good finish.
Sirspeedy, I'm sure the loving care you give your speakers is worthwhile, but I believe you are repairing the finish itself (a la your comments about finish checking), not the wood underneath. Unless the finish was poor to begin with, the wood underneath is fine, as it is protected from the elements, as it were. Finishes are subjected to the elements, however, and olde-style finishes do age, lose moisture and resiliency. Modern finishes are pretty darn inert and only need to be kept clean. I'm in agreement with S7horton and Merganser. (I do think that an application of real Carnauba wax is useful some places; no furniture oils or polishes for me, though.)