Trick to get cruft clean filesystem like new gentoo install

[defer-]

Hi, i have had gentoo installed for a long time. Its working great but it would be nice to clean up old cruft from filesystem left by me. I wonder if this method would work for getting clean filesystem just like new gentoo install? If it should work, i would appreciate suggestions on how to accomplish this in practice. After figuring out how to do it, i will try it and post results and detailed guide here.

1. Backup configs and files you want to save.
2. Do emerge -e world install to new folder like /newroot
3. Clean / and move /newroot to /. Reboot. So now you should have clean filesystem just like new install, right?
4. Now you can copy/edit/patch configs you want to edit and files you want to save.

Would this method get you a clean gentoo install with your custom settings and packages? Ideas or suggestions?

[Gentoo64]

Depends what the cruft is. Could be anything :s

You shouldn't have random files laying around much in / except configs (which you'd back up anyway) if it's leftovers from stuff you uninstalled maybe just clear out some stuff in /home/.config /etc /var /root and sometimes remove any groups that were created for that package. I find the easiest way is to just clean it out manually, should only take ~10mins but I'm not sure what type of mess you're gathering.

I have a habit of constantly checking things are how they are supposed to be, stuff like:
cleaning unused files / folders
rc-update show
gcc-config
alsamixer
kernel config
eselect * list
make.conf

I like doing general checks just to make sure things haven't changed for whatever reason, keeps my system pretty clean.