It appears that one of the items on your car that is most susceptible to the elements and sun or UV damage is the convertible top. Without proper care they will fade, stain, yellow and crack similar to cloudy headlights. If this condition is not checked and allowed to worsen eventually expensive replacement will be the only option. There is an alternative which is restoration of the convertible top. Just like with headlight restoration, an item that was previously replaced at great expense can now easily be restored to like new condition.
Before proceeding with this article, be sure to check your owners manual for required car as some convertible tops are more sensitive or may require special products or coatings for maximum durability. If you do not already have an owners manual one can easily be purchased through your local new car dealer (for older models they may have to order it as it probably will not be in stock). It is also a good idea to have the owners manual anyway so you know the correct maintenance intervals, safety issues and everything you need to know related to your car.