It's not a matter of how many people use it, it's a matter of fair distribution with a deflationary currency.
Hoarding WILL be an issue if a huge influx of users ever arrives at some point, driving both demand and prices up.
The shifting of the decimal will be easier the more evenly distributed the currency becomes. Many people are very weary of buying BTC in general. A client/miner will allow the average Joe to download a simple program and start earning some BTC. Obviously there are tons of scenarios that could potentially unfold, but a deflationary bubble is a very real possibility. I think one of the best means of counteracting a deflationary bubble is to widely distribute the currency in it's early stages.
That is silly. Mining is buying coins. You are buying them by electricity, risk, depreciating capital equipment, and skill.
Most computers can't mine, most cases are ill suited for mining, many users have inefficient systems and high electrical costs. Users killing their computers, mining $100 in BTC using $300 in electricity, or blowing circuit breakers isn't likely to increase adoption.
Not sure where you get the idea that more mining would reduce hoarding. You can buy coins today on the exchanges. That is proof that coins are available for sale.
Mining is not buying coins. It is a bit like buying coins with a hardware hedge, but it is not buying them. More miners also = increased network strength which is a benefit no matter how you look at it.
While it is true mining is impractical for many people, this is only true because of 1) aforementioned GPU arms race and 2) current price. But if (when) a huge new influx of users arrives, demand and price will go up.
I'm pulling figures out of nothing here, but lets say 1 BTC gets distributed to each of 2,000,000 new users/miners slowly. It will be a lot better in terms of market stability if these 2,000,000 new users already had 1 BTC floating around in their account rather than if 2,000,000 new users scrambled to buy 1 BTC each all at once. In the latter scenario there could be a supply problem with a greater incentive to hoard; in the former case there is none.
And yes, I realize this a vast oversimplification. I'm isolating contexts hardcore.
From your response, reverse doesn't work either 