If you show me a dead orc all I can tell you that it is a orc and that it is dead. If you tell me that you found it in the middle of a cave then I can say it is adventurer's kill, if you said that it was found in a hill giant's kitchen then I would say it was a meal. What I am talking about is context. By looking at the context, the story of what happened can be told. The difference between an adventurer's kill and a meal.
The same with building strongholds. If all you go by are the rules, then folks are crunching numbers, with some adventures as they clear out the region hex by hex. Boring to some. However add culture and religion into the campaign then building strongholds becomes something more. The interactions between the different cultures, religions, and the players will generate conflict, conflict means adventures; epic adventures.
The addition of culture, and religion provides the context to make the building of the stronghold meaningful. If this is part of your campaign from the beginning then by the time that players are building their strongholds then they are invested in one or more of the factions that make up the various cultures and religions of your setting. They will have ready made reasons for building that stronghold, and to expand it.
And you don't need much either. You don't need to write the equivalent of the Similarrion and the Appendixes to the Return of the King. What important that you write down the right ideas, the ones that lead to conflict, the ones that lead to adventures. And add enough to make the proceeding stuff make sense so that the player can connect the dots on their own without you having to spoon feed them.
At low level, adding this stuff allows you to give treasures other than gold and magic items. The favor of the king can be just as useful as the +1 sword found in the dungeon. It makes your hireling and henchmens more interesting by giving details about their background.
If you not interested in culture and religion then building strongholds will be boring as hell. Better to come up with a different endgame like tripping out to the planes.
This post was prompt by this thread on Knight-n-Knaves.