Edit: To clarify this was meant for level 50 characters synced in pre-50 dungeons. The stale trash>door>trash>boss mechanic in 50+ dungeons has varying levels of tomes as rewards already. The low level dungeons only give tomes when done during roulette. That is not going to make someone choose to run a low level dungeon as a level 50 when they have done there roulette already. There needs to be some form of incentive players will want to get them to run these dungeons wihout joining a party with a friend or through roulette.
Recently I have decided to level another job. Surprisingly, I have found dungeon running quite enjoyable. I truly did not expect this after completing a relic. The big difference was gaining experience points.
Now, as a 50 you just want to get in and get out, as you gain nothing from killing the mobs on the way and the loot is usually irrelevant to you. But as a pre-50, I don't care if someone wants to pull the whole dungeon, I am getting experience for each kill anyways, and that is my point in being there.
If they could convert that experience into some form of points we could use to "buy" tomestones (our choice of which to buy), there would actually be a reason for people to want to slow down and kill everything, and not just try to rush to the end and get out.
Say 2.5k exp=1 point. Let you store up to 1000 points
100 points to buy 100 soldiery
500 points to buy 100 poetics.
100 points to buy Alexandrite map
50 points to buy an AF augment part
50 points to buy tier 2 materia
100 points to buy a tier 3 materia
Possibilities are pretty endless. Cycling items in and out of sale could also be used to alleviate duty finder queue based on an influx of new players. Free trial weekend? No problem, just add tier 4 crafting materia for sale this weekend to get a lot of people running dungeons for the new players. Almost anything...the point is to make running a pre-50 dungeon and killing things post 50 have some meaning.
Anyways, just an idea. Post yours, it is probably better then mine.