US Airways is back with a 100% bonus on purchased miles in January, but it looks as though the bonus is only available to folks who purchased miles in 2012.

A couple of years ago US Airways Dividend Miles picked up some new tools that lets them target their purchase miles bonuses and do some better analytics. And since then they’ve done both broad-based bonuses and targeted ones.

To find out if you’re eligible, go to the purchase miles page and you’ll be asked to provide your name and US Airways account number, so they can verify whether or not to offer you the bonus.

Then assuming you qualify you will be shown the offer.

Even with the 100% bonus, after the federal 7.5% tax, you’re still paying almost 1.9 cents per mile.

That’s great for topping off towards an award. Or if you find award space available in business class to say Hong Kong you can straight up buy that award for $1700.

But in most cases I wouldn’t buy the miles speculatively — to hold for future use rather than for an award you’ll be ticketing now — because I do think that the US Airways award chart is ‘ripe’ for a devaluation. There’s been much speculation about a revenue-based program for US Airways. It’s been three years since the award chart had major changes. I suspect if anything is holding back changes it’s the potential merger with American. So while I think in the immediate term US Airways Dividend Miles will hold their value, I don’t see buying miles as a worthwhile long-term play.