While I agree that the wording is indeed vague, you will have a fight on your hands asking insurance to pay for a new mast if you can't prove that the rigging is less than 10 or 15 years old.
The phrase " reasonable steps to preserve" protects the insurance company from having to cover your loss if you have very old wire rigging. If you are "reasonable" you follow "Industry Standards" that are widely accepted.
You can google "service life of standing rigging" and similar phrases, and find plenty of published maintenance recommendations. They're easily found. some are written experts who design and manufacture rigging
See, for example, this presentation from Navtec Rigging:
standard yacht standing rigging service in denia
www.slideshare.net
.
Or this one from Rigworks:
Guidelines are not quite as clear cut as "replace every 10 years" for wire rope rigging, but most of them say 10 (souther)-15 (northern) years on both coasts, 15-20 for inland freshwater boats, Service life for wire rigging is considerably shorter in the tropical climates, or 40-60,000 miles (or one circumnavigation), or whichever comes first. Rod rigging service life is usually said to be about 15-20 years, with a inspection every 5 or 6 years, or 40-60K miles, whichever comes first. Leaving the mast up during winter storage contributes to metal fatigue, so you don't get credit for winter layup unless you drop the rig and store it inside out of the elements.
If I'm going to pay for insurance to cover damage to my boat, I'm going to maintain it according to requirements. Otherwise, the property loss insurance is worthless because the insurance company won't pay. They always will always cover damage to my boat caused by "operator error" (like running aground, for example), but it's much less certain when it comes to rigs, which have a finite service life.