For the record, this debate occurs more than just the realm of FRC. If you walk the pits in FSAE, you can hear similar debates over "monocoque" vs. "spaceframe" designs. and there are very reasonable arguments that can be made eaither direction.
http://www.fsae.com/forums/showthrea...(stressed-skin)
It should be noted though that most Formula Cars, which are often looked at as the pinacle of performance engineering end up going with Carbon fiber "monocoque" designs. But they have evolved into those over many years, and arguably great performance was found using other methods before.
In FRC, I have observed equally awesome chassis design using plate and spacer, sheet metal, and stick/tube frame, and hybrid.
I will say a lot of very good teams use a slowly evolving chassis design from year to year, and thus optimize their design a little bit better. This gives them a "proven" platform to support the most basic need for most games "move". I believe/suspect that this allows them to spend more time/talent on end effector and manipulator development as they are not consistently re-inventing the wheel.
Other teams re-invent the drive base each year, but this does come at a heavy design resources cost.
Ultimately a well thought out XXX design that the team has had success with will usually be out poorly developed "superior construction method" chassis that has little development time on it.