1000 DASH for collateral is extremely high. The current 6% reward is barely enough of an incentive IMO.
It isn't 6% reward it's 45% and 50%-60% after Spork 21.
You must be thinking of ROI but you've even got that wrong because you've denominated it in Dash which is incorrect. ROI is denominated in the currency invested, so if you invest dollars in a masternode you measure your ROI as the value of your investment at the end of the year minus the value at the start all divided by the value at the start (and all measured n dollars).
That means you have to take into account the capital gain or loss of the collateral. The 6% would only apply if we were a stable coin.
If the masternode (~60%) reward, coming straight out of the blockchain, causes the whole chain to devalue then masternodes will have a NEGATIVE ROI. Your 6% will get wiped out in an instant. So it's important to optimise the reward ration for capital gain, not to maximise masternode reward in Dash. That's just the way to make everybody poor.
To me the right direction would be to make changes to double the masternode count, thus encouraging new growth and further decentralization.
You can't base the viability of the coin on masternode growth. It needs to work for the equilibrium condition, where the network is stable otherwise when it hits that condition the price will just crash (like it did the last time. Now we're struggling to even reach escape velocity because all the rewards are being pocketed instead of going towards upwards difficulty adjustments).