Great post! i had some issues getting this to work on raspian stretch. As others reported i too had problems with libboost1.55. I did not find any solution in the comments here. What solved the issue for me was to add the xenial instead of the trusty packages.

so change this:

    deb http://ppa.launchpad.net/gridcoin/gridcoin-stable/ubuntu trusty main
    deb-src http://ppa.launchpad.net/gridcoin/gridcoin-stable/ubuntu trusty main

to:

    deb http://ppa.launchpad.net/gridcoin/gridcoin-stable/ubuntu xenial main
    deb-src http://ppa.launchpad.net/gridcoin/gridcoin-stable/ubuntu xenial main

in `/etc/apt/sources.list.d/gridcoin-stable.list`