Sorry but I'm not going to cheer a new ATH.
More masternodes mean that an ever-increasing percentage of Dash is held to secure masternodes. This means that it is likely in "strong hands" who aren't going to be willing to sell (even in an uptrend--overlay the masternode graph with the recent rise from .0125 to .0195 and you'll see very few people cashed out). Consequently, the supply of Dash on the markets decreases, so in the face of stable demand, the price of Dash increases.
tl;dr Every new masternode is 1000 fewer Dash on the market. Less supply = higher prices.
P.S. It's mostly ASICs that have decreased the ROI on masternodes. We are permanently at minimum block reward, which was not the case before.