My 98 has 28000 miles, would changing the friction material be worthwhile just because it's old even though it works fine?
I think you've answered your own question there. I replaced the parts in mine because it was not functioning as it should, being grabby. If your clutch works fine then I'd suggest saving the money and spending it on tires or beer instead. I don't think "age" has much to do with whether these components need to be replaced but if it makes you feel better, don't let me stop you.