Aside from the cost savings, the other goal of reusing boosters is to reduce the time between launches.

The challenge for SpaceX is to inspect the booster, integrate a new second stage & payload, and relaunch in a few weeks. With a few years of work, it should be almost like a cargo jet turnaround.

ULA's Vulcan plan is to parachute the engines and pumps back, catch the rope with a helicopter, inspect and reattach to a new set of tanks. That seems likely to be a little more complex to me.

The catching with a helicopter part is complex, but not time-consuming - either it works or it doesn't. The rest is probably if anything easier - I'd imagine SpaceX will have to tear down the booster entirely for inspection, at least for the first few hundred. These things are (or will be) built to be disassembled and reassembled, attaching engines and pumps to a new tank is not going to be a long and complex process.