If I ever built a keep, the next thing I’ll do is ask the DM to have some Big Bag take it from me so I can go into exile, vowing to reclaim it some day. That would be cool.
Oh, that’d be nice! Like a bag of holding, but big enough to keep your castle in it.
I’m not sure, I think it’s more fun to blow the DM’s mind when it comes to keeps. I recall once we cleared a massive Castle based (very loosely) on the Castlevania - and it was out in the moors, with just a few surrounding villages that had been abandoned.
I decided, after the adventure to KEEP it. No one else claimed the territory, it had lots of gimmicks and the peasants would be happy to have the support (I was a highish level cleric, once a week I’d do free healing and create food and water as a feast).
Granted, hiring enough staff to defend, keep and clean, and refurbish the thing was a money sink in it’s own right, but damn it was cool. 
Most of my friends though preferred the whole Dragonlance option to open a “keep” as a inn/bar/tavern and make money from it, while always having reserved rooms open between travels.