Absolutelly great! With Sparx Enterprise Architect you can model UML and also take advantage of the Use Case Metrics. Using metrics in software developement projects is essential!
It would also be possible using the function point (FP) method or a pretty complicated COCOMO process. But why not using a pragmatic approach?
Doing a easy categorization of use cases in "Easy", "Medium" or "Difficult" doesn't take much time. At the end just do in EA menu:
PROJECT - Use Case Metrics :
Links to USE CASE METRICS
http://parlezuml.com/blog/?postid=263 about Use Cases & Scenarios