The only people buying a full sim's worth of Nautilus are speculators and resellers. One reason I would rather own regular mainland... I can terraform and subdivide that land, which you can't do in Nautilus. I can also expand out of a 1024 sqm footprint, which I can't do in Nautilus (unless I buy another high priced lot adjacent to me for 120,000)
As for buying land and hoping to make a profit from reselling it. Hey, that's just as risky in RL as it is in SL. I own almost a full sim of mainland too, but most of my mainland has recouped it's purchase price because the stores I put on it turn a profit. This pays my tier and covers the purchase price of the land in a few weeks.
So it really depends on what you're doing with your land. If you're not running a business on it then don't expect to make money. Like in RL, if you have a vacant lot sitting there, you still have to pay taxes on it and clean up after anyone who dumps there or be fined. If you try to sell it, you're not going to get much unless someone really needs it for something, then you can name your price. The same seems to hold true in SL.