I have some small houses in random areas just to teleport to to mine, harvest wood, or other resources. Just a workbench inside. Teleporter is outside. No walls, no nothing. Just house and often a boat docked next to house on the shore, all within range of my one workbench. Nothing has been broken or destroyed. Ever. I even leave the doors opened as well, as I never really bothered to close them, since it made it easier to run in and out.

My main house and my 2ndary house by the shore are the only ones that are walled off and with multiple workbenches scattered around the premises. Mind you, every bench is roofed or inside to protect it from the elements. No mobs have ever spawned inside, nothings been destroyed. Only my main house has the Odin ward stone built, which warns me when my walls are getting hit, but it's usually mobs missing their ranged attacks on other mobs and it hitting my defensive walls instead. That and not all my land is flattened, some of it is still just the way I found it, grassed and all.

Just my experience with the base and mobs near my bases. Only time I've had mobs spawn or attack me in the open was in the base I set up to grow flax in the plains. Deathquitos, lol, just flew over my fences and started attacking me, but they're flyers so that doesn't count. :D From my experience, even when mobs spawn outside my walls or near my base, they don't aggro me because the walls prevent them from hearing or seeing me, which is how it's suppose to work from what I've seen and read.