Currently, raids are just annoying. They really get in the way of many gameplay styles such as base building or just relaxing at home. If players want danger, they can just leave their base and go where the monsters be.
In the early game, I would often be in the middle of building something enjoyably, and then be annoyingly forced to waste 2 minutes kiting enemies around in the early game until the raid is over. Great, I am now being punished for enjoying the game with a mechanic that just gets in the way.
These leads to silly solutions like building earth walls to prevent raids from being a problem. This also inadvertently forces raids to be weak because a "surprise event" that leads to high probability of death and a destroyed base is bad game design.
What if we could manage expectations properly with a soft event countdown. There are two ways to do this:
1. A (!) symbol on the map at the raid location saying something like "The trolls will attack in 5 days" or "An event will occur in 1-3 days" without specifying what the event will be.
This would allow players to prepare (even mentally) and make raids fun because you can plan for them. If you are in the middle of a build – you have a buffer that allows you to finish what you are doing or plan to pick it up after the raid.
2. A moving raid that originates somewhere and moves towards your base gaining strength as it approaches.
You can choose to meet the raid en route while it is still weak and engage there, but outside the safety of your walls. Or you can prepare for them at your base, and defend a stronger raid but with better defenses. This allows the player to choose how they want to approach raids – enhancing player choice. It also allows the player to choose the difficulty.
There should be some nifty reward for defeating the full strength raid at home that you forfeit if you choose to defeat it beforehand.
With well-managed expectations, raids can be harder and more elaborate – because the player gets to choose the harder raid if they want. Because you know a raid is coming ahead of time, you can also get some friends to hop into a server and turn it into a group event.
PS: My personal preference is that the probability of raids should be tuned to how peaceful the player is being. The probability of a raid should be proportional to how many of those corresponding enemies the player has recently killed.