"Realms that go to war often tend to have surplus nobles"? Seriously? Where on earth do you get that from? Because that's not my experience at all. What, you simply declare war and, poof, 20 nobles appear? It doesn't work that way. When you have almost as many nobles as you have regions, no, there are not "always regions to be acquired".
When the regions at your borders already suffer from anarchists due to distance from the capital, no, there are not "always regions to be acquired".
Realms that go to war tend to be exciting. Exciting realms tend to attract players. On Dwilight, the realms with player shortages are all very peaceful, while those with large surpluses are all very warlike.
If a realm is so big that it cannot expand, then it can consider dividing it's lands so that it can.
I don't know where you play, but you must always consider that food affects the different continents very differently. Some continents have only realms with surpluses, or just about, while in others, very few realms have steady (although significant) surpluses. On Dwi, basically you have a few realms which really need food (D'Hara, mostly), a bunch of realms that pretty much break even (surplus is so small they don't like the risk associated with sales), and a few realms with have so much surpluses that nobody really needs to bother with the trading game at all and that very little can convince them to actually care.
If the realms on Dwilight are unwilling to sell their surplus food, then increasing the price cap on trade would be a good way of encouraging them.
