I don't know what to say if the spawn blockers aren't working, but as far as looks and aggro goes, once you get the spacing correct using workbenches, you can replace the ones you don't want with campfires. They don't have to be lit. They're not as ugly as workbenches and they only draw revenge aggro, like if the mob is mad because it can't reach you.

If you are trying to cover a large area, it's possible for things to spawn in before the anti-spawn items load, so I've heard. Mine usually work in my base, but I did have a shaman show up once.