A luxo golf course on some of Florida's most expensive real estate. I think that's called a "First world problem" but YMMV.

Mar-a-Lago doesn't have a golf course.

But it's probably worth more than that.

No, it's not. You're kidding with the Boca Raton comparison, right? The Boca Raton consists of 337 acres (20 times the size of Mar-a-Lago), has a 1,047 room hotel (which Mar-a-Lago doesn't have), a golf course and a full marina (which Mar-a-Lago doesn't have), a 50K square foot spa and health club (which Mar-a-Lago doesn't have), more than a dozen restaurants and bars and 200,000 s.f. of convention space (which....well, you know).

Mar-a-Lago can't be used as a hotel or resort. It can only be used as a private membership club. They can't expand it, they can't subdivide it, and they can't change the use. The historic designation makes it subpar for a luxury single-family home (very high-net worth people want to do their own thing); the highly restrictive zoning and small size makes it subpar for a resort (it can't be used as a hotel and it doesn't have the size for the amenities you need).

This is why despite the fact that there's lots of real estate brokers willing to mouth off to the press with ridiculous comps (the Boca Raton? Really?), you didn't have any appraisers saying under oath that it was worth $400-600M.