Have you ever used https://rails-assets.org/ ?
Mint 17. I totally forgot to comment here again, my previous comment about the folder sharing using rsync sudenly stopped working...
Nice guide. A few weeks ago I tried following it but ran into a few problems with chef recipes but now it worked =)
Only two small problems:
1 - My "bundler" gem was not installed by vagrant, everything else worked fine
2 - Webrick was veeeeeeery slow, after a few google searches I saw someone saying that its because of the vbox sync, so I added this line do the Vagrantfile "config.vm.synced_folder ".", "/vagrant", type: "rsync"", now it runs almost as fast as on my local machine.