Determine the purchase price for a leasehold property

Well, the standard land value is the benchmark for an undeveloped plot.

The standard land value has nothing to do with development (commercial properties etc. excepted). The developed property has the same price as the developed property.
And you buy the land and terminate the leasehold agreement. So you buy the groundlease-free plot.
You won't have to pay any other price than the land value according to the standard land value and possibly a surcharge.

We pay an annual ground lease interest of about 0.7% based on the standard land value.

The ground lease interest can also be adjusted.

I don't think there will be many external interested buyers for such a plot.

Why not? Buy land and set it aside (regularly increase the ground lease interest). After 52 years, the children/grandchildren of the foresighted buyer have a plot.

I would simply let the contract run as lessor and make the most of the interest in the future...

Which would also be completely fine for us. As I said, we don't have to buy, we are very satisfied as it is. The owner approached us.

The standard land value has nothing to do with development (commercial plots etc. excepted). The developed plot has the same price as the developed plot.
And you buy the plot and terminate the hereditary building right contract. So you buy the plot free of hereditary building interest.
You will not have to pay any price other than the land value according to the standard land value and possibly a surcharge.

Which purchase price is agreed upon is ultimately a matter of negotiation. It can certainly also be below the standard land value if the owner cooperates. And of course, an undeveloped plot has a different (higher) market value than a developed plot. That should be obvious.

The hereditary building interest can also be adjusted.

Yes, the lessor of the hereditary building right can also gladly do that. The conditions are contractually fixed. As mentioned, the last time this happened was in 2005.

Why not? Buy the plot and put it aside (regularly increase the hereditary building interest). After 52 years, the children/grandchildren of the foresighted buyer will own a plot.

Because an interest rate of 0.7% on an investment of 200-300 k€ will likely appear quite unprofitable to many. There are far better investment opportunities. And after 52 years, the grandchild then has the option to acquire a plot, provided they are willing to buy the house standing on it from our grandchildren at market value.

Nothing is as trivial as it may seem at first glance. Therefore, I would be interested in experience reports from someone who has subsequently bought out a hereditary building right plot.

And of course, an undeveloped plot of land has a different (higher) market value than a developed plot of land. That should be obvious.

NO! Just believe it when someone whose job has been this for over 20 years tells you.

Otherwise, please explain "of course" and "That should be obvious." I always like to learn more when I structure financings and deal with property valuations.

Because an interest rate of 0.7% on an investment of 200-300 k€ may seem quite unprofitable to many.

Plus the appreciation of the land, many are speculating on that. When I see that some condominiums have a realistic (not broker-advertised) return of 2% (including vacancies, renovations during tenant turnover, etc.), I don't find a worry-free 0.7% that bad at all. Also note, if your lease is tied to the rent index (2005=88.5; 2020=106.9), the lessor can increase it by 20% tomorrow.

At least in the local property market report, the BRW for developed plots must be adjusted from the possible floor area ratio to the actual floor area ratio. That means a very large plot built with a small house (but it could be much more) results in a calculated discount in the BRW. At least that's how it goes into the appraisal reports.

Otherwise (with the same floor area ratio as in the BRW map) I completely agree with you.