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Another point that hasn't been made yet, at least not as I see it, is that it takes a lot of miles to upgrade that trip. For example, on AA, upgrading from full-fare economy to business between the U.S. and Japan takes 15,000 miles each way; from discount economy, it's 25,000 miles each way plus $300 co-pay. (IMHO a co-pay is fairer than making you buy a higher fare class from the get-go just to be in the lottery, where you're out the difference even if your upgrade doesn't clear, but that's a separate issue.) Earning 15,000 miles, if you start with no status, takes three North American trans-continental round trips. So the entire question of upgrades is moot until you've flown for a while.

You can get miles for things like taking out credit cards and opening a Netflix account, but you have to be pretty single-minded in pursuing lots of those bonus offers to get enough that way.

You can also buy miles from some airlines, but that's an expensive way to get them - though not compared to a business-class fare - and the annual limit may not be high enough for your needs.