Dungeons - it is content that has just been abandoned, new players never really get to do all the content since there is nearly noone doing it and the people that do are just wanting speed clears and actually making this content more worthwhile will not only bring more players back to dungeons but allow more new player to experience the content.
New Dungeons - we need other dungeon content, not just the boss rush "Strikes" doing this we could add in raid mechanics to allow aspiring raider to get a better understanding of what they will need to do in actual raids ofcourse toned down versions otherwise there would be no challenge for the actual raids.
In doing all this it will flesh out the existing content and give people more to do daily, since I know there are alot of people who log in maybe 1-3 days a week depending on there raid groups, finish there raids then exit till next week.