The prototype pictured is great. More importantly, the point made is dead-on. Prototypes should be fast and inexpensive demonstations of feasibility and testbeds for gathering engineering data. They should be no more sophisticated than they need to be for these purposes.
The time issue becomes especially critical for build-season prototypes. The clock is ticking!
Downingtown Area Robotics includes 15 VEX teams (in addition to FRC Team 1640 and 6 FLL Teams). We have very successfully used VEX parts for fast prototyping in the past (and expect to continue to do so in the future). VEX parts are not suitable for every prototyping need, but they have a good range of utility.
We prototyped a Pivot drive during the summer of 2009 using VEX parts to work out control strategies. We mounted a cRIO and other FRC control components directly on-board (battery was teathered). Photo below.
