It's harder and harder for people like us, but there is a TON of money out there. And with pooled masternodes, like said above, people will continue to invest in something with a great return. Right now, the return is very good, but big money makes 20% a year regularly. When DASH matures, and the volatility is diminished, 5% per year interest will be considered good to a lot of people, except big money. Those large holders will bail: slowly, over time, because they will have better opportunities than this. The percentage of rewards are balancing out until we hit 60%, then the percentage will definitely drop as more masternodes go online. Plus, each year the mining rewards diminish.
Lets watch those masternodes, we'll see when they start to give up and sell off. I'm sure they'll sell off slowly, not huge dumps so I don't want anyone thinking there will be a huge panic dump in the future, that would be a stupid move for an investor.
I'm not sure I quite understand your logic here. As I understand, investors of small amounts of money need to find high-risk/high-ROI to grow their money faster. Large investors, on the other hand, seek out places to safely park their money and get a modest but respectable interest. If the ROI for running a masternode goes down to 5% and volatility in Dash is diminished, then only the BIG players will be masternode holders and the small players would bail. The small time guys would only keep their money in a Dash pooled masternode earning 5% like a savings account, untill they took it out (of the masternode status) to invest their Dash (directly!) in something riskier, like a business startup, house, stocks, etc.
RE masternode sell-off, if the price keeps rising and adoption keeps growing, there will be fewer and fewer reasons to "sell-off" into another currency such as BTC or fiat. Someone saving Dash in a masternode might liquidate it to buy a car or a house, but if the purchase is made with Dash directly, then this would not really affect the exchange rate.