I think you are pretty conservative here.
Despite the adaption rate will decline when the majority of the masses have adopted bitcoin as their currency, the inflation is also getting lower. Therefore I think 10 000 % increase after each blockhalving is actually quite realistic. That means, the current blockhalving should result price of around 60 000 usd/btc sometime in the coming years. The block halving of 2020 will make the price to millions of dollars per bitcoin so 2030 holding even 0.1 btc should be able to make you a millionaire not to mention of holding 10 btc.
The advantage of owning more bitcoins is sooner millionaire status.