It is a good idea. However the current Wi-Fi systems are operating under the infamous Part 15 dark cloud umbrella. The reason why a 1 watt power level is allowed is because of the frequencies used and would not be useful at all at lower levels.
Then of course there is the issues of cordless phones and other devices that utilize the same piece of spectrum as the Wi-Fi routers do. Even with the implementation of the higher frequencies those too are filling up fast.
I think that although its a good idea, it will end up being shut down because someone's cordless phone or alarm system or baby monitor or wireless router will be interfered with.
And we all know that the good ol Federal Communications Controllers will not allocate a piece of the massive and ever expanding upward spectrum to dedicated Wi-Fi setups such as this. However if there was a way to tax and fee every connect and charge a utilization rate in the same fashion as a gas pump runs the price meter with amount fueled, they might actually do it.
RFB