$2,500 Upgradeable Delta Fares NYC-Tokyo
There is a common misnomer that using miles to upgrade paid fares is the most lucrative way to spend your miles. While it may make sense in some situations, most airlines have instituted hefty co-pays and/or it's only the most expensive coach fares to eligible for international upgrades.
Delta is known for being the stingiest when it come to upgrading international fares - you need to buy the most expensive coach fares (Y, B, or M), which sometimes are even more expensive than discount (I) business class seats. To add insult to injury, many times upgrades aren't confirmable at the time of booking, so you need to cross your fingers and hope it clears before departure. I never recommend going that route - I'd personally rather book the cheapest coach fare and then "buy up" if upgrade space becomes available.
I still have some Platinum Medallion Upgrade certificates back from the day when Delta automatically gave them to Platinums, but when checking the international market for upgradeable M fares, I usually see $2,700- $3,200 for Europe trips, which is a little too rich for me - especially since you only get business class. As I wrote about in October, Delta does have a good relationship with Air France where you can use a PMU or miles to upgrade Air France Premium Economy, (which is around $1,300 off-peak and $2,000 peak for JFK-CDG), which I may do this summer.
However, I'd really like to visit Asia soon, so I checked the NYC to Tokyo route and discovered they have some pretty reasonable M fares that are loaded from now throughout the year for around $2,500. They even include the Haneda route, which currently has a double miles promotion.
So for $2,500 you could fly LGA-DTW- HND confirmed in business class for 2 Systemwide Upgrades or 50,000 miles. As a Diamond, I'd earn:
SkyMiles (not elite)
13, 858 base miles
6,929 M class 50% bonus
12, 854 for the double miles promo between DTW-HND
13, 858 Diamond bonus
Medallion (Elite) Qualifying Miles
13, 858 base distance
6,929 M class 50% bonus
This isn't a "true" mileage run because I'd be paying $2,500 for 20,787 Elite miles - 12 cents a piece - when good mileage runs are in the 3 cents range. I could route through a couple more cities to squeeze in more miles, but the best it will get is around 10 cents a mile.
However, it is a fantastic way to go to Asia in comfort and accrue a boatload of redeemable and elite miles. Even if you don't have system-wide upgrade certificates, you'd be earning almost as many miles as you are using for the upgrade. So in essence, you are getting a $6,000+ business class fare for $2,500!