I'd say if you were going to buy that amount of bitcoin, you'd have the patience to spread the buy orders out over more than a few days. People with lots of money do basically the same thing in the stock market all the time. It's certainly possible to buy thousands of bitcoins without moving the market much--I think it would just take patience and tons of cash.
What you describe is sometimes executed as an Iceberg order.
You see only the tip of the iceberg. In the background is a bot that keeps putting up buy orders as they are executed. Since a bot does it, it can do this all day, putting up buy orders every 5 minutes, ... watching the order books and not putting in 10 million all at once.
If it's not a bot, it's a built in functionality of the exchange or brokerage or whatever you're using. I find that a bot works better since you control it, but if an exchange has that kind of thing in place, that's cool too.
As for buying at a premium, well, for one, you get government guaranteed coins, you don't need to mix them anymore as they are declared clean and anyone can trace it came from the auction. So, it can, in theory, be sold at a premium too, for those looking to buy so called "virgin" coins.
On the other hand, if you were just to HODL it, it's very clear you can declare the price you paid for it, and the price you would sell it later, and there'd be very little or no questions about the capital gains or taxes or anything of that sort.
One could take advantage of the gov coins, coin join them with a whole bunch of other coins gotten from other places or deals, and they'd all be considered as connected to the gov coins, and you could then sell them all later at profit. Or just hold on to them for the next ten years.