I cannot remember the last time I paid for a ticket. (only kidding. I have but not a lot and not lately)

^ to promos, ^ to credit cards, ^ to tips and tricks and schemes found in places like FT !

I would pay for a domestic ticket if it were say $250 or less to fly from Bos-LAX or an international one if it were say $350-400 to fly BOS-AMS, but generally I use miles when I fly.

I would say it depends on your money situation and how much you do to get new miles to make it easier to work with them. If it's hard, then paying may be easier.