As an educational toy, sure... The only practical use I see there is laser etching. I don't think it would make a useful 3d printer, for $500 you can get a dedicated printer that would be much better. The resolution doesn't seem like it would be good enough for P&P, except for larger discretes. The robot is only part of a P&P system, you also need vacuum system, a good vision system, plus software. Again, $500 would buy a pretty decent cartesian frame which would be a better base for a P&P.
Perhaps with good vision system and software, the resolution of the arm could be compensated for, at the cost of reducing speed, and I did think to see how far such a system could be pushed. Probably much of the system developed could be transferred to a better motion platform later.