To me an airline promo should either -

Make me buy a ticket I don't need, for miles I do.
Make me choose you on my routing instead of the opposition.

Be it price or mileage promo, it should be simple.

Sell me a Sat/Sun C class ticket for a bargain price on a last minute promo. I don't need it, but at that price for the miles, I'll take one. Your domestic and DUB/BRU cabins are empty most of the time. LX do it most weekends and it's highly successful.

Give me double or triple miles, not this fly X, get Y, especially when Y isn't miles.

Oh, and when you do have a promo, please don't make me jump thru hoops to claim my prize.

OT: Don't give me a perk like GUV's, and then make it difficult to use them or make me feel like a sponger for wanting to; and load a couple of extra meals on flights just in case we do succeed.