It can vary. There's either a lot to do, or very little. It all really depends on what you find fun and motivating to do once you hit 70. There are plenty of options once you do hit 70 on your main though. As noted above, it all depends on what you find interesting. The main motivation for dungeons at 70 are usually either for tomestones, Wondrous Tales, and alt job leveling, followed pretty closely by helping other players. The great thing about this community is that there are a lot of players who do all kinds of things, so for the most part, you'll usually be able to ask for advice/help on whatever it is you want to do at max level. Just keep in mind that you still have about 3 more patches of story to go through after you complete 4.0.