Speaker maintenence. When to re-foam etc.

I like to shop for second hand equipment and have been looking at some older Watt Puppies.
At what age is it time to consider maintenence?
There are too many variables, humidity, use and so forth...but that beind said 10-15 years maybe...it just depends
The speakers I'm interested in are about 9 years old.
Is it difficult or expensive to re foam the speakers?
Does it change performance?
NO, NO AND NO...I have a pair of 25 yr old Towers and they sound great..if you dont want to fuss with it look up little stereo shops in your area...shouldnt cost much either