Probably both 
Nivemus always has plans, but I've never seen a single one being executed 
Some plans worked.
Remember the Duchy of Kalmar? It belonged to OI one day and it belongs to Nivemus today.
I trust you all dont remember, except OI players. How Brock managed to get duchy of Kalmar without much drop of blood and soldiers casualties? That show you how good diplomacy skill Brock has. Brock would have killed OI long ago, before that ice thing came and changed whole things. OI former Emperor willing to let his lands absorbed into Nivemus, that pretty much tell you something about Brock, don't you?
How Catherine had to literally war with OI to gain Duchy of Kazakh. Brock followed her footsteps to gain a duchy(which totally bring Nivemus into lands administration problems). At a near future, Nivemus will have to secede some duchies to form a new realm. So join Nivemus if you plan to be in the new realm or just plain stay in Nivemus.
But what power do you in turn hold in Nivemus? 
His character has
Unlimited power in Nivemus. Granted at one point, Brock will have to step down. He has been Ruler long enough. Once the new realm is formed in Nivemus, he will step down. I see no further stories to develop with Brock. He has done what can be expected of him.
Brock cannot hold back the progress of other nobles. I see plenty opportunities in Nivemus. Some longest characters like Jason hold some sway in Nivemus, even Judge sides with him recently for those who know in Nivemus
