Personally, I'd put up with a 50 watt device that only gets a watt to my phone. I'm pretty sure that's doable with a smart transmitter and small receiver.
And that in turn does not take into account the real efficiencies involved, I would be highly surprised if a device like the one you described had even a 2% efficiency.
See my other reply, I don't need anywhere near 1 watt average for my phone.
When I see a report from MIT of a 1 foot receiving coil running at 20% efficiency at 7 feet, I don't see what's unreasonable about a phone receiver beating 2%. I said at the start I wasn't talking about using undirected transmission.
Don't know about your, but my phone tends to draw ~2.4W when idle with screen on, and I'm pretty sure it stays over 1W even with screen off. That watt would, like 'gamesbrainiac said only make it lose charge more slowly.
And that's just one phone. My household has 4, not counting other mobile devices like tablets and Kindles. Putting a 2% efficient (!) power system to use seems like a crazy and absolutely scary idea. Just multiply that over the number of potential users (~2 billions).
Also, 98% of this energy will have to go somewhere. It probably means heat.
But the only time my phone drains 1 watt with the screen off is when it's doing cellular data transfers with a terrible signal. It has an 8 watt-hour battery and it lasts more than 8 days when I toss it on a shelf to wait for calls.
So if my phone's sitting there using 1/25 of a watt, a 2% efficient maintenance charge only costs 2 watts. And we can do much better than 2%.