Yes.
No. Dungeon and mob balance in dungeons -- including boss mechanics -- are balanced around 1 tank, 1 heal, 2 dd. Changing these up means that in many cases substantive alterations of mechanics would have to be present. This includes, but is not limited to, room size, spawn number and frequency, damage output, health, and move sequences. As an example, on the boss Demon Wall, you are given a narrow bridge and a clock to kill him, two gnat spawns, and the rate of wall advancement is pretty quick even though one has to deal with gnats and advancement. Changing these up to "balance" around a particular setup and gear-equivalency, and still be challenging, would require more substantive work than just upping numbers and whatnot. Every dungeon would have to be changed.2. Party size increased to 6
Some, not all, are not very efficient for leveling (e.g., Haukke Manor), though many (e.g., the first three) are. You'd have to find some evidence where dungeon experience is slacking and bring it up to par, or where the game is not providing enough options to make up for the slack. In some cases, the lower dungeon experience provided can be due to a larger resource for experience in and around that level range. With Haukke, there is a large series of story quests involved, and taking these into account is likely why the dungeon is so sparing on experience. But once you've done the dungeons on your main job, what next? FATEs. At this point, the Costa del Sol FATEs are extremely lucrative, with Cancer popping ~2.5 hours and the rest being very, very easy to do and frequent. Escorting the hooker is always fun.3. More xp for dungeons
Svara, Behemoth, Odin, Dark Designs, Highbridge. There are several "raid-like" FATEs, but they act as either FATE chains, or mechanical monstrosities. Love them. There are also Cancer, Lazy Lawrence, Steropes, and the Negotiators>Hide & Seek>The Coeurl King FATE chain in South Shroud, along with the defense/breach of the Hive. These involve special mechanical "big" bosses with their own "big boss" music.4. Fate raids (very very difficult, require 50+ people) implemented and requires zone-wide activities
Vanity slots are confirmed, though not for when. Phials of Fantasia will do everything else you need, and one is available to you as soon as you subscribed for one or more months. (You really shouldn't need to keep using one -- use the character creator and save a character model for yourself and tweak it until you LIKE it, then when you get a Phial, load that model for your redesign.)5. Character customizations like name change, race change and vanity slots!