Regarding the false dichotomy of old content vs. new content: both are required to make a solid game that will last and keep holding the attention of the player base. My raid team of lvl 55's has enjoyed running Denova Nightmare Mode in the past just because the tight mechanics are a nice challenge. It's fun to see how well we can work together as a team when we're up against something that cannot simply be outgeared
Level 55 nightmare ops are not able to be outgeared currently. Do those if you want a challenge, they're relevant.
This is not a false dilemma. Man hours are limited, new content keeps people playing more than old.