Except that land is fundamentally different from Bitcoin mining. It is more closely analogous to Bitcoins themselves. Buying lots of them is increasingly expensive, and is only possible currently due to the relatively low price. Land is already expensive, and I would wager there simply does not exist enough capital to purchase an entire continent, or possibly even a few states, and certainly, that much capital isn't in a single person's hands. You are fearing something that is, frankly, impossible. And even if it were, the answer to a feared concentration of power is not a concentration of power.
And yes, your actions on even a small plot of land do indeed affect all future owners of that land. This is reflected in the reduction, or increase, in the value of the land. A blasted wasteland is not worth as much as a verdant forest, even assuming that the creation of that blasted wasteland from the verdant forest doesn't effect - and thus, incur damages from - other people's properties. (Which is not a valid assumption.)
In many places of the world, land is extremely cheap. Right now China, Western Europe, the US -- basically the rich countries of the world are buying up farmland in Africa, Ukraine East Asia -- basically the poor places. Private hedge funds are buying up large chunks as well. See
this. So some people will control large amounts of land - and even today land is distributed very unequally. I don't see how one can dispute this.
The reason why land is more analogous to bitcoin mining rather than to bitcoins, is that through controlling mining, you can affect the entire bitcoin community. If you just have a lot of bitcoins, you could play with the price to some extent, but you cannot cancel people's transactions. However when you control land, you have a very direct control over many other peoples' lives. You could poison their water supply for example. Sure people could go live somewhere else, and if land had an infinite supply then my argument would be bunk, but the earth is limited and we all have to share it. Your actions on your piece of land affect the community at large. Spending your privately owned bitcoins is not the same.
If you have ever shared a small house with a number of people, you would see where Libertarianism breaks down. Your argument about providing incentives to maintain land value is IMO not very strong. What if I can make more profit from destroying the land than maintaining it? What if I am old and I have no children and I don't care about it? What if I am just a psychopathic person who likes destroying things? What if I am just selfish and don't care about others or the future? There are many reasons why someone could choose to destroy a piece of land. Wasting money in some irrrational way is not the same.