If you know where you might like to fly, but don't yet have a chance to do so (/know when), then you could perhaps book 'flex plus' flights with the miles (+ taxes) and then once you have specific dates move you should be able to move the date for free (assuming there is reward flight availability for that date and at that time)... I think as long as you have travelled within a year of ticket issue date you are free to change as you please?
Not sure if that's a helpful option?