Related to Gary's point, is the concern I had that neither MPL or Beagle were returning engineering data during critical phases of EDL.

I like Gary's notion of a probability curve, and the difference between a craft that will function only in a narrow window of possible scenarios, and those which are more tolerant.

If you are going to draw inferences about whether you should continue to use a design, modify it, or junk it, you need DATA.

If you failed, did you fail because of a fundamental flaw in the design, a random equipment failure, or set of environmental conditions you couldn't handle? If the latter, just how far off a nominal profile were you?

If you succeed, was it an easy success, or did you surivive despite conditions at the edge of your envelope?

Without any sort of data return, we have no to know what inference to draw. Even WITH lots of engineering data there's only so much you can conclude based on a single success or failure, but it sure beats nothing.

For all we know, MPL and Beagle actually worked but both landed on big sharp boulders.

I do actually fault the way both of those programs were structured, but especially Beagle. If I recall correctly, Pillinger sold it as a possible model for future low cost missions. Fling a dozen of them all over Mars for less than the cost of two MERs.

That's not a bad idea actually, but unfortunatley, it means that the first one devotes top priority to proving the EDL system. So maybe you carry little if any science but do carry extra accelerometers and gyros, data recorders, some sort of system to transmit basic data during entry (like the "tones" from MER). If it works, great, send 10 next time with the science package. If not, you have a good place to start from to figure out how to fix it.

If you do posit that you can only fund the first one if it carries the full science package, not much test equipment, then go ahead and take the gamble, but don't claim it is any sort of prototype, much less part of a "program".