Hi ben,
My it is not like you to be pessimistic. They have now rasped the ice and proven the technique to get a sample in the scoop. They have opened the doors which they said they would do 2 days before taking the real sample. All is on track and in the hands of true professionals. Don't be 
be 
I don't think this is pure water ice, rather it would probably be a permafrost combination of as yet unknown material. (ice, salts, dust and who knows what else). We don't even know how the ice was laid down. Atmospheric deposition in the past, runoff, frozen water table?
A small sample is just as good as a large sample to detect organic traces. And I would stress the organics rather than life. ie Methane is a simple organic compound but does not require biology. The TEGA and Mass Spectrometer in combination are a clever design. The temperature of the sample can be correlated to the volatile release to aid in identification and the MS can measure the isotope ratios of C, N, O, H, Ne, Ar, Kr, and Xe. You may have already seen the link below. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1780.pdf
The wet chemistry lab has already provided a wealth of data on the soil If knowledge is considered important then the mission has already been of great value.
