Sandboxes need builders. With no builders, they may have literally nothing.
In real life it is easy to destroy and hard to build. It can take days to build a simple wood house. A couple minutes with some gas and a match can remove that. Building, we must fight gravity and entropy. Destroying, they are our allies.
So I leave this thought: for a sandbox MMO to be successful on the scale of WoW, building must be faster, easier, and more common than destroying. Note that when I say "on the scale of WoW" I mean millions of subscribers, not necessarily 11 million. Or alternatively, equivalent profits from a freemium system as if it were a million+ subscription.
Minecraft fits somewhat what I mean. Building can be very time-consuming, but getting TNT is a huge pain. With creative use of waterfalls of lava or water there can be a great bit of destruction, but at the same time, creative use of them can protect structures.
Over the long long term, building and destruction should balance out. It would be as absurd to have an infinitely built-up world. Eventually the buildings should fall. And then we build over the ruins, before we create more ruins.
My experience in EVE may influence this. I was a noob, one who farmed poorly and probably didn't have anything right in terms of ship choice, loadout, or character stats. It took a while to get my ship. Farming and finding and then getting it back to where I farmed. Then it went boom in oh... two hits. The second hit was my pod. Destruction took five seconds at most.
Slow to rise, quick to fall, is painful.
Also, read this by Tobold.
[Landmark] The Endless Beta
8 hours ago