Very true - a machine, although useful, plays a limited role in improving one's game. Great for working on mechanics and practicing situation-specific shots, but that's about it.
The volley is also great for overheads. I cut a few pieces of a 2X4 and nailed them on top of one another (3 to be exact). I brake the rear wheels, then place my little gizmo underneath the axle for the front wheel to tilt the machine back to produce very realistic lobs.
Need help finding lost dog: walks with a limp, recently castrated, can only see out of one eye - answers to the name, "Lucky".