Have you set up your revenue cycle modeler? If you haven't, there are some samples in there from Marketo. I typically set up 2--one for leads and one for customers, so you can see where everyone is by stage. Once you have this set up, you can run reports, directly from the modeler. If you have opportunity as a stage, you can run an analyzer on that particular stage.
Here's the general info/deep dive: https://community.marketo.com/MarketoArticle?id=kA050000000KyvFCAS
Once you approve your model, everyone will fall into a stage and you can run reports. Granted, the best reporting comes from RCA, but I don't believe that's avilable in spark, but if its something your company wants to see, probably worth the upgrade! 🙂
Hope that helps!