I'm not a Mach3 user, so I'm pretty out of touch with what it can do over and above the basics. From what I read, though, it's interesting that there seem to be more add-ons for a piece of commercial software than for something open-source like LinuxCNC. 3D printing is a pretty obvious area to extend it.
For me, the interesting bit of the printer was building the thing, and just buying bits would have taken all the fun out of it! But then, I've just designed and built a microprocessor temperature controller for an old soldering iron I rescued from a skip, when I could have gone out and bought one from Maplin for, relatively speaking, peanuts. I used my 3D printer to make bits for the router, and I'm now thinking about a new and improved printer that I could build now I have the router available - or maybe I just need to build the mk2 router first and do a better job... I know I could build a seriously good extruder with CNC machining available!
Be interesting to see what you discover in your researches, and where the crossover points between additive and subtractive machining are these days.