So back to this thread:
1) My good friend and unpaid consultant Brodie helped me go through electrical troubleshooting. Everything seemed good in terms of connections and contact, and matched the expectations provided in Bergmen's guide.
2) However there was a small voltage on the purple line with the brake light NOT activated, precisely 61mV. This lead me to believe that similar to other notifications on the forum, this was preventing the system from engaging the cruise control.
3) I did purchase a relay to install - I found a nice place under the left side panel to install the relay using an existing screw.
After install, I took it out for a test drive and voila! - cruise back in order, so no need to upgrade to a Gen 3 ES (darn it and happy at the same time)!
Thanks so much to Brodie and Bergmen for their help in getting to the bottom of it, and to the collective of the forum who pointed me in the right direction from the start.