Yeh, I think VSTO is a view of whats to come, I can see vba staying as it is and ultimately being replaced by a .Net type environment soultion, maybe as user-friendly as vba, maybe not.
I agree, Office is an end user environment but then they stuck vba on the end of it and made it a development tool too. I think many vba developers do it as a secondary function to their jobs, I used to have to code in secret at my last place. I think MS will continue support for vba for a long time yet, and move new development to a .Net type of environment much like the change from dialogs to userforms in the past, albeit on a different scale. Whatever they choose to do, I look forward to it, there could be a fair chunk of freelance work coming out of it