Parts do wear, so upgrading is a natural option. I just replaced the original RX100 rear derail on my '91 Peugeot Success with a new 105. Chain too. Shifting is much crisper & easier, feels like a new bike.

Replaced the steel fork with aluminum (on sale from the LBS) about 8 years ago after a wreck. Put on a triple crank about 6 years ago, & a new Mavic wheelset (the front wheel had also been trashed in the wreck). Keeps the thrill alive!