Sabayon is constantly being updated and, as long as you keep on top of the updates, there is no need to re-install. I am using Sabayon 5.2 to write this but it started as Sabayon 5.0. The package management system "Entropy" makes it quite painless.
Self-righteousness is a loud din raised to drown the voice of guilt within us - Eric Hoffer
Don't believe what it says on the right - I am anything but sagely; More oniony!