Of course, with more nodes, the ROI will be lower.
But, adding the SmartRewards on top of rewards from nodes, it will still be profitable even with a much higher pool of nodes.
With InstantPay being implemented and hopefully integrated with merchants, along with more exchanges, the price will hopefully rise. Not only making it more profitable, but also make it more costly to set up new nodes and thus, slowing down the increase of nodes.
I look forward to see how the future plans out :D