I've wondered the same thing about my relatively worthless skymiles. But I just discovered their new (?) marketplace site and found you can get some excellent value out of your miles via hotels. You might check this option out...
https://travelmarketplace.delta.com/travel/arc.cfm
They have tons of hotel choices nearly anywhere in the world and in places where my Starwood or Hilton points are of no help. Now, instead of avoiding skymiles earnings I may just go for more knowing I can use them this way.
There are other merchandise purchasing options too but I think for me, the hotel option is the way to go.
Haven't checked into the car rental option yet but I'm sure most any of these options will be easier to get value from compared with their pitiful flight awards.