The only reason people are getting involved is because they know that there is a limit. Who in their right mind would invest in something that will be diluted infinitely? The price of bitcoins would still be at $0.001 if there was an infinite supply. An infinite supply mean that no matter the demand, the price is going to be tiny, because there will always be more.
The first is just your opinion (Which is fine), the later is misleading and untrue, because demand could rise with supply, bear human population growing rate in mind.
Yes, you are right. It all depends on the growth rate vs adoption rate I suppose. I guess there could be no limit but it grows really slowly. If it grew linearly, we would almost be in the same position as now, as growth is expected to be exponential in the long term (even if also small). But still, I don't think people would look at small growth, or linear growth the same way they look at a fixed amount. Psychologically speaking, I know I am getting a permanent piece of the pie when I buy/mine bitcoins, and that is why I do it.