The level 49 dungeon gives 300k experience for completion. Level 51 dungeons give 400k experience for completion. Level 50 dungeons give 0 experience for completion, and 150kish if you duty roulette.
So, what is the point to doing them if you don't have them unlocked and you have a new character?
Appearance Gear?
Nope, the new 52-59 gear is the same gear from the older zones, and they can be dyed! You can cheaply buy full sets for less then 100k gil.
Give Stat Gear?
Nope, the new level 50 main storyline quest gives way better gear now. The gear from these dungeons are worthless.
Experience?
Nope, older and newer dungeons are better. Don't even need to roulette them its a bonus. Plus if you get the older dungeons in the low level que its the experience + the roulette bonus.
Law?
Neverreap and Fractal give 80 Law, and possibility of a bonus. If you do Expert you can get 80+40+80. Whilst the high level que can only give 100 max. You also have to wait longer doing high level ques.
So, even though its not pointless.. Its worse.
Fun?
Well, I love doing them. However I can't because I need to level my alt and doing them is a waste of my time.
I just do not see a point to these dungeons as they are. There is no reason why they don't reward experience. These zones are fun and deserve to be ran, not be worthless content. Please consider this and thank you for reading. =)