Why not have a two tiered approach.
Option 1: run a full bitcoin node with a fixed number of spr, preventing nodes from ever going offline while not capping the total number of bitcoin nodes in existence and allowing servicenodes to continuously receive rewards.
Option 2: dynamic servicenodes for users providing less resource dependent services like instant transactions, private messaging, etc. Allows for greater ease of setup than masternodes (run multiple servicenodes from the qt client with the click of a button). This market would likely dictate that the cost of doing so is higher than running a bitcoin node but would be a strong incentive for newcomers and bagholders alike to maintain a strong position in the coin.
Also, if you didn't know, in Spreadcoin you can have multiple servicenodes for cheaper. So I don't really know what you're on about.
the ability to have mutiple servicenodes is and should be an aspiration.
but having too many in the hands of a few works against the network - it becomes less decentralised.
in my provided example, it would still be incredibly decentralized when factoring in the bitcoin node operators. If spreadcoin is going to be successful, it's going to because of the potential for profitability. If it's less feasible for large holders to run multiple servicenode instances, this may drive price downward as the incentive to hold diminishes. Where would bitcoin or dash be without the whales?