A spacer lift doesn't get the same travel as an actual suspension lift. You still have stock articulation or may a little less, but jsut an inch higher because of the spacer.
Suspension lifts with longer springs, longer shocks, and new UCA's are where you can start getting more flex.
UCA's aren't necessarily required, but are suggested when getting a 3" lift for alignment reason. Also, when switch over to a uniball setup you can gain more droop as a ball joint style UCA may bind while drooping.
CV shafts do play a limiting factor, but thats when you start getting into the long-travel stuff.