I have a 2000 Boxster. Original Top-13 years old. Car is driven daily in all seasons as my primary car. High mileage. Raced and tracked.
Never garaged or car covered. Top is in excellent condition. No water proofing needed.
I can say I speak for all Boxster owners. I never heard of a top going bad or ripping.
However, the story is different for the windows. The 97-02 models had rear plastic windows while the 03-04 models had glass rear window.
The glass rear window is smaller than the plastic window so you lose visibility.
The plastic window cracks if you try to lower the top in colder weather. Below 70 F degrees. When it cracks, a shop would charge you $300-500 to replace the rear plastic window. Colder weather makes the plastic brittle while warm weather makes it easily bendable.
To replace the entire top, it costs $1900 at Porsche, less at other shops. You can also buy a removable hardtop for $1500, or a used one for $1000.
Porsche Boxsters are galvanized so they don't rust either. I have never seen a Boxster or 996 911 with rust.