About the price, It's 1 DASH = 1 DASH I guess? They do not based it on the fiat value of the coin. It's the same with people saying 1 BTC = 1 BTC.
When you look at the Dash ANN when price was over $1400 in 2017, I'm pretty sure these questions have been raised and answered already. It doesn't look like they are in a hurry add more with over 4000 active Dash MN.
Yes. A few people making decisions on the network, would make DASH utterly centralized. After all, not everyone can afford a DASH masternode. I'd prefer cryptocurrencies that are driven by developers and the community as a whole than just a group of wealthy people that will lead the network towards their own interests. 1 DASH may be equal to 1 DASH, but most people use Fiat to determine a cryptocurrency's value. Not changing the collateral according to market price, will leave many people out of the system.
I'm surprised to know that there are well above 4,000 masternodes on the DASH blockchain. That's a lot of money if you consider DASH's current price on the market. Imagine how much a masternode will be worth if DASH goes back to $1k? It'll be insane! At least, the project is open source. Thanks to this, we now have various masternode-based cryptocurrencies. I'd put my money into other masternode coins that are focused on decentralization above all else. Ultimately, the market will decide whenever DASH will remain the leading masternode-based coin or go all the way down the drain. I wouldn't worry about DASH's centralization since there are plenty of options to choose from. Just my opinion