Happens to the best of us. Once your borders and heartlands are secure and you remove a few rival factions, what is there is stop you ? It's not like you have to adapt your army over time, because you pretty much have the same force throughout the campaign, which you already used to achieve victory after victory earlier. No civil wars or massive events to worry about either.

I reached 42 regions once, but after that, I tend to restart after 30-40 years. It's actually been months since my last campaign effort. My campaign game is in an unplayable state. I'm hoping when I finish modding it'll add some interest to the campaign beyond the 30 year point, where interest begins to wane.

The add-on sounds a bit more interesting campaign wise, but then again, if it turns out to be nothing but more than the same, I shall weep before playing something else instead. Minesweeper perhaps.