
I dunno what to say as to the ideas validity, it would be neat, for sure.
In order to control and breed a good community you could do it this way:
Players have to be a certain level and meet certain requirements before they can get their own kingdom. Before they have a kingdom they can work for other kingdoms as part of their monster killing, world exporing, resource gathering, inside training arenas or kingdom vs kingdom battle teams.
You make it so that a kingdom is best run with 3 or 4 other high level teams in it, teams that decline to make their own kingdom - and the more active lower level teams, the better. You provide incentives of loyalty and rivalry to keep players from starting their own kingdoms if possible.
You make gold prices for advances in the kingdom incredibly high priced so to make the strategy of what to get in what order all important.
Also, you do not allow your kingdoms to MAKE money(with things like alchemists guilds etc), apart from perhaps gambling on who will win in a kingdom vs kingdom battle.
The incentives for making your own kingdom should still be visible despite this - and yet not everyone should wish to do it. Players that don't play all the time, and those who have a decent "rank" (you rank members of your kingdom) in the kingdom they are serving will find it better to stay supporting their kingdom. Those with a low rank and play often - when ready can branch off, take a couple friends with them and start their own new kingdom.
The kingdom is almost like a guild, the identity being the key thing. You can rank kingdoms by "influence" - the most playing time by members, battles won vs battles lost etc.
The other thing kingdoms could give easily is training. Like sean says you could do training at a price - but my idea is slightly different. You could do training, and train by playing "friendly" battles with other members of your kingdom against AI opponents who drop no items, but give extra experience. Even training in friendly PvP vs your kingdoms other members.
The kingdom must by houses for each of it's members, and can upgrade training facility for extra benefits, as well as upgrading its weapon shop and herb shop for extra benefits.
i'm just waffling and repeating a lot of what you're saying sean, but i saw your cry for help and thought i'd give it a go.
Most of it is just shooting the breeze, but at least it's there to spark ideas.