If this has been requested before I apologize in advance. Have you ever thought about having the strongholds rebuild themselves over time to give people things to do? They could even get stronger.
Yeah. It's been suggested. Also been suggested that they would remain available until you 3* them. Midoki has said they might do something about it, but no real confirmation.
There are going to be a few more Forts and Strongholds added to the current Exploration Map... soon. We're also looking at allowing people to replay bases until they've been 3*d, but unfortunately that will be less soon.
@Lynsey [Midoki] have you all ever thought about having them respawn after a cooldown period? You could possibly have a randomizer that would create strongholds based off of existing user maps that are out there. Different levels that pop up, you destroy them they cool down for a day or something like that so it's not an endless thing you can do farming all day long off of them. It would at least give another form of game play and income. Also it could make a way for people to practice attacking. Just a thought.
We're planning on implementing a set of PvE bases that change each week, which I think would be what you're after?
Ah sorry, MMORPG terminology creeping in there! PvP - player versus player (competing against other players) PvE - player versus environment (competing against game controlled content)