I too have Citimiles. I've used them a few times in the past and the flights were mile for mile. Now it's 2500 miles minimum and $15.00 handling fee. The airlines or the reward companies only "purchase" or are awarded a certain number of seats on each flight and that's understandable, I think. But if you book early enough, as I have recently the seats are usually available unless it's during a holiday or big event. My advice is to have several definitive flight plans when you call for reservations.
My biggest beef, us that you cannot upgrade your seats and once you book it, you're done. No changes, no refunds!
Once I use up my miles, I'm changing credit cards to get more bang for my buck! Good luck!