Seeing as how node is single threaded, If I have node server running on an amazon EC2 instance with 4 EC2 Compute units will it run any faster / handle more load than if I have 2 EC2 Compute units?
Does CPU utilization on amazon require a program to be multithreaded to fully use all resources?
The reason is that node.js uses an event loop for processing, so if all you are doing is starting up a single node.js process without anything else, it will not be multi-threaded and thus not use more than one CPU (core).
However, you can use the node.js cluster API to fork the node process so you can take advantage of multiple CPUs (cores): https://nodejs.org/docs/latest/api/cluster.html. If you write your code that way, then having more compute units will help you.
There is one caveat, in that EC2 compute units are detailed per instance. For some instances you can get more "compute units" per virtual core. So if you pick an instance that has 2 compute units per virtual core versus one that has one per core, you will be able to execute node on a CPU that has more compute units. However, it looks like after 2 compute units the computing power is split per core which means you won't get any benefit from the multiple cores.