"The key to bootstrapping this capability is the judicious use of robotic precursor missions. Robotic spacecraft are now orbiting the Moon, mapping the distribution of elements such as hydrogen and ascertaining the nature of the environment near the poles. The next steps are to measure the composition and physical properties of the polar deposits from the surface; this requires soft-landers capable of landing payloads on the order of a few to tens of kilograms. Small surface rovers would be able to map out the elemental concentration of volatiles and determine the best places to mine.

After the prospects are mapped, we must experiment with different techniques for harvesting and processing. Again, this work can be done by modestly sized robotic missions, landing small excavators and trucks (Mars rover-sized) and using laboratory bench-scale processing equipment. Landing and experimentation with this equipment will allow us to find out which techniques are most effective, what processing methods use the least amounts of energy and have the highest yields, and determine where the choke-points are in the processing and production stream.

These small initial steps allow us to begin extracting and storing resources immediately. Over time, we can increase these capabilities such that when people finally return to the Moon, they have at their disposal a cached accumulation of consumables, including air, water and rocket propellant. In effect, we are creating the initial phases of self-sufficiency even before human arrival through the emplacement and use of automated, robotic infrastructure."
http://blogs.airspacemag.com/moon/

I think mining on a small scale is critical aspect regarding beginning to mine in space.
But I think there two different things here.
One is prototype mining- which doesn't need to be concerned about the operation itself of producing
enough material to be profitable.
In other words to be profitable one would have get say 100 tons of product for every ton required to be delivered to the moon to get the 100 tons.
So this prototype purpose is to demonstrate that some similar mining operation could get a predicable
result. So if you send 2 tons of stuff and it can mine 1 ton of lunar material and say extract 10 kg of water, that could be considered a success. Whether it goes on to mine a ton or more of water could seen as a bonus.

The other kind of small scale would have to with their not being a market and this market needs time to develop. So small scale in this sense may less than 50 tons of water [or whatever] being produced the first year- this matters whether it is profitable.