The Uldah trend for me started with the November update. Soloing Cobs and Dobs combined with leve linking Broken Water made Thalan the place to be, for battlecraft and thus the central market was born there too. While I like your ideas about having boons in your home city, I feel other things need to be done, before we can even start to think about breaking the Uldah as a main and only city problem (if you call it a problem, a few of my ls members with far more MMO experience than me have said, one city always naturallly becomes the main city). He are just a few thing I would like to see happen:

Economy:

The wards need to have a request button. An option to purchase an item from a ward in another city. I think you would still get regional differences in price, but the request option will mean if you set up your retainer in Limsa, it is not lost to the Uldah/Gridania players. I think without this you cannot break the central market, because players will feel their wares will not be viewed by enough people and in some cases anyone. It is also my belief that this should be the final evolution of the wards to being a fully functional market system. The only additions I would make then would be to how they look.

Battlecraft:

If I had wrote this a few months ago I would have said to nerf the cobs and dobs in some way and I am glad this has been done. They are still an affective grind for a duo (not nearly as affective as linking but affective).

The other thing which still remains is the linking. I think two things need to occur here. Firstly camps need to be brought into line with each other. Each camp should have a set number of leves, I would personally put this number at 8, maybe 10, but I feel 10 would make linking a bit too rare. At later leves each city should have a power leveling camp and a marks/credits camp. This would make it so certain camps are no longer better than others. Also if players would looking for credits/marks, they would travel to each areas camp to get them, same for players looking for power leveling. Finally and this is contraversial, to make this system work, would require the end to fail partying. At each reset the completed/failed leves in your journal are taken away and you start again afresh. For me the arugement of losing 1k of marks is not enough, it is pretty easy to get the marks you need just by ranking up to 50 and doing leves on easy difficulty solo, or with friends. The end of fail parties would make players travel to the best camp for their party. They would go where the links where, which brings me back to having 8 leves per camp. With this number you be able to get good links, whereas with 10 leves you would make linking a rarish event.

In conclusion these are two things I would try to do to spread the playerbase out. However, it is worth noting that right now the playerbase is low and maybe other cities will be brought more into the game by a population increase. Also the opening of Ishgard could cause a redistribution of the population as well. I do however, feel tht the ability to request items from retainers in other cities wards is essential. Without it there will always be a desire to have a centralised market place, through fear of of wares not being viewed by potential buyers.