Still gets to keep the house but has to pay extra monthly - and the coin probably appreciated more than the house - but who sells these? I would probably want to spend money on owning more coins than the one, but that is me- everyone collects differently, and I can respect the different ways that people view this hobby.
A 10-20% better coin for a 2000% increase in price... I usually try to maximize the quality-to-price ratio, so the best-of-the-best coin would not be an attractive purchase for me (unless of course money was no object).
I understand this perspective very well. When I purchased my Caligula ADLOCVT sestertius in 2010, I could not imagine another one that was markedly better in detail and other aspects. But the one that sold for $635K four years later is indeed such a coin -- maybe 25% - 50% better in most aspects, although I think the artistry of the portrait and reverse is pretty much equal for both coins. Would I want to pay a 10X premium for what is perhaps one of the finest Roman sestertii in existence? Probably not, since I have many other coins to chase and spending $800K (including buyer's fee) on one coin puts a serious damper on one's coin budget. So I continue to pursue my collecting objectives knowing that the decision of buying the "best of its type" is probably not an objective that's at the top of my criteria.