I don't think there is a rush to create more and more features that no-one needs ... Roles is a structural thing that consolidates hundreds of different feature requests into one system - it'll make a LOT of things easier in future. Likewise the XMLdb feature simplifies things for developers and increases stability.
I couldn't agree more about focusing more on testing and QA, but sometimes we have to go where the funding is. Few people want to fund developers for testing and QA, so I need to find that money from elsewhere. The process for this has improved markedly in the past few months since we set up the tracker, by the way.
Currently in 1.8 our focus
is totally on smaller
usability issues, and a long list of fixes/cleanups (not new features) (see
MDL-7396) because people are in fact paying us to work on that.

.
About the gradebook, the planned
gradebook rewrite was last week costed at US$45,000. I really would like to see it done for 1.8 but we need to find that funding (or someone good to step up and volunteer their own time). Perhaps you can ask your university.