@mitu Thanks a lot.
This saves me a lot of time, preparing an rsync just for those folders and ignoring entirely /usr, /bin, etc.
I also noticed the existence of /home/pi/.emulationstation that includes stuff like the "scraped" game images, but I found it to be a link to /opt/retropie/configs/all/emulationstation .
I also noticed that the .state files are stored inside the "roms" folders, in the same subfolder than the rom itself.
Thanks and best regards.