Yeah, the idea of using a stencil for undressed stone makes me think of texture tiling in video games. Looks good when you're standing right up next to a thing, but when seen from a distance, the the illusion dies a quick and ugly death.
It's not just the grid repetition that gives it away. Natural irregularity has fractal scalabilty: step back from the pattern, and you see meta-patterns of irregularity. Wheres simulated "randomness" using one-note methods tends to dither into an unnaturally homogeneous field when you step back. The sequence my be non-repeating, but the distribution averages out much too evenly.
For brickwork though the stencils looks brilliant.
The method Neldoreth posted, and variations thereof, do not seem that time consuming to me. You're basically just drawing a grid with a ruler, then going over the whole thing with a texture stamp. It could get a lot more time consuming depending on the masonry pattern and how rough you wanted the stonework to be, but at the simple end like what Neldoreth shows, seems like it wouldn't be hardly more time consuming than the stencil stuff.