"why can't I just use programmable LED strip lights that are already wired together and have a microcontroller at each node?"
I think you can.
These are digitally controllable,
they have an arduino library
(see downloads tab)
Build up some minimal inexpensive clones
http://store.nkcelectronics.com/arduino-runtime-board-rev-b.html
populating as little as you need.
Run 120V the length of your driveway, with 5V wallwart at each node to power the arduino and light strip.