You could do what the EU does, and make the upper house consist of the state governors. That way, for the upper house to approve an increase in federal authority, they actually have to vote to move power from themselves, as individuals, to the lower house (this is a part of why the EU is relatively unimportant compared to the constituent EU nations).
Except that senators were not popularly elected, but elected by the state legislature (so corruption was easier). Sending the governors themselves to DC would shift powers back to the state (a good thing, imo), but governors wouldn't have much time left for governance.
I think we could improve upon on current system by adding a vice-governor to the governor's ticket, and subjecting the ticket to the popular vote. Then the governor could send the vice-governor, his popularly elected subordinate, to Congress, which would help shift power back to the states. As it currently stands, senators do not feel a need to pay heed to their states' governors.
I'd say the power to leave is also a nice feature, it forces the larger government to provide some sort of value and not step on too many toes or risk being disbanded.
Imagine if California was free to regulate all of healthcare for itself. They could write whatever socialized medicine program the voters desired all while not burdening the people of Texas with the cost who perhaps prefer a free market solution of some kind. As different states implement different programs people would be able to vote with their feet as to what was the better deal, causing states to compete with one another to offer the best deals to its population.
States are too small to effectively implement what they want? That isn't a problem as they can contract with each other and if that goes south look to the federal government to resolve the dispute.
