I think people will just focus on trading their crypto currency since, like you said, mining will be more expensive than the Bitcoin you'll actually mine. I also hooe that by the time we rea h the 21 million mark, that we can see a huge stabilization of price of bitcoin so it could be adopted in the near future.
When the limit comes of bitcoin mining and no more mining, the price will go higher and higher because if the demand increases and there are no bitcoin available in the market, the price will definitely increase. When more and more companies and shopping malls accept bitcoin as their payments, the use of bitcoin will increase and so the demand and so the price.