Definitely new tub, cast iron is great.

Makes sense that finish won't last. I guess what I'm asking though...the finish won't last on an acrylic tub either. The cast iron tub I may just have to refinish again in 10-15 years, but the acrylic tub I would likely need to replace altogether in 10-15 years. Am I thinking about that correctly?

Why acrylic tub? Buy a new cast iron one, and it should last a very long time. I wouldnt refinish an old one, since that may last 2 yrs if you are lucky. Do it right once, and you shouldnt have to do it again.

The finish on an acrylic or fiberglass tub is not as durable as a porcelain/enamel finish on cast iron, period. The aesthetics of an acrylic or fiberglass tub is typically not as detailed as on an old cast iron.

A couple things. First, make sure you understand the difference between a steel tub and a cast iron tub - they are not the same. With stamped steel, you get what you pay for, and even expensive ones still don't equal the quality of a cast iron.

With a new cast iron, your cost will meet or substantially exceed the cost of refinishing an old one.

Refinishing can be near-to-factory when performed on site. However, to do that the tub should be fully exposed, meaning all walls and fixtures removed to completely expose it. But if you go to that length, then the better way is to deliver the tub to the refinisher's shop, and the finish will equal a factory finish. There they will have better opportunity for prep, which is the key to refinishing.