Use of inexpensive MEMS accels as instrumentation-grade sensors

We use high quality tri-axial DC-accels ("instrumentation-grade") for in-vehicle (automotive industry) measurements of steering-response motions and vibrations. These accels cost approximately $1000-$1500 each.  Some are MEMS based and come in a variety of packages approximately 1inch - 2inch in size.  We have an application that requires hundreds of accels and are considering using inexpensive accels like Analog Devices model no ADXL335. Comparison of performance specifications between the ADXL335 and our instrumentation grade accels shows comparable performance, yet the price differential is large.  We have also evaluated the frequency response of the ADXL335 vs the iinstrumentation grade on a calibration stand yielding favorable responses. [1] Why is the cost differential so large?, We understand that the ADXL335 is offered as a chip instead of the ruggedized, encased packaging of the instrumentation grade accels, but the cost differential still does not appear to be justified if the packaging and documented calibration are the only differences.  [2] Is there a difference in the fundamental performance of "instrumentation-grade" accels and these ADXL335s?, [3] Are all MEMS-based accels similar in performance? We desire direct access to an expert who can discuss this comparison of the inexpensive MEMS accels(vs instrumentation grade).  We have discussed this question with an application engineer at Analog Devices, who could not answer these questions and suggested that we post the questions at this site.