packs have been constructed out of cells with very closely matched capacities

On that note, the fewer cells connected in series (ie: the lower the overall voltage of the pack), the less troublesome cell mismatching is.

I don't know about current RC practices, but from a battery lifespan perspective, the best arrangement would be very few cells in series, and separate monitoring of each cell (or set of cells in series), with an electronic power management system to draw from each cell what it can provide, and aggregate the outputs (with voltage inverters as needed) to supply the load. That way, each cell gives what it can, and the power management system keeps each cell operating in its optimal range.

More complex to implement, but it would allow you to get all the power that is in there (minus parasitic losses in the power management and inverter circuits), yet not abuse the individual batteries, thereby maximizing lifespan.

Do any RC systems use a smart power management system in the vehicle?

Do any of them regulate (voltage boost) power output, such that MORE power can be delivered to the motor near the end of the race, despite the rising internal resistance of the batteries?