the wire goes for 15 years, 20 years, the rope maybe 8.
You have to factor in the cost x 2 because you'll have to replace it twice as often.
Racing and trailer - sure it makes sense. Most boats, not so much.
Not true at all. About 90% of the cost of switching the first time is buying the reusable fittings. After that the rest of the cost is the line itself. So your first time it is about the same price as wire, after that it gets really cheap to replace when necessary.
Also note that 8 years is what is currently being recomended from Colligio (I believe) which is the same replacement interval for stainless fittings like turnbuckles and shackles on your standing rigging.