Not really. The problem is what you see as data can often be used to control code without modifying it. It doesn't have to run directly on the processor to end up being as powerful as code. You often find don't have to modify code to use the code the code that's already there to do what you please. This is true of a surprisingly large portion of modern exploits. A strict Harvard Architecture or the NX bit only helps with what is becoming an increasingly narrow portion of the attack surface.

Again, see also: Python, PDF, Javascript, CSS for a few different types of "data" which end up being as powerful as code.