Speaking as a pure amateur
I think the debate has polarized around caution vs poor interpretation of the information. However please bear with me. I fly more than 250K miles both as a revenue and non-rev passenger each year.
I think there is a clear case here for one thing - MORE RESEARCH. My argument is that judging from the data from D-CMET the concentrations of ash vary widely even at the predicted levels. Therefore it would be safe to conclude that the mathematical models combined with met info are not sufficient to make cast iron decisions. Reading through this thread the vast majority of people agree. Neither do I think the decisions left to the Pilots alone is a safe decision - they are not being provided with enough tools to make the "right" decision. Despite a significant amount of data that points to the damage that can be done, the impact of lesser concentrations of ash remain hard to comprehend. The hard data tends to deal with the catastrophic type situations (BA009, NASA's DC8 and the F/A18s).
We also know that we are dealing with the shades of grey. Personally I would feel a lot better if there were better ways to continue to measure the particulate concentration at the different flight levels, with the goal of creating/establishing some safe corridors and flight profiles on a real time basis. We have seen from the Germans that these concentrations of ash are not consistent at particular flight levels therefore to continue flying constant flight levels may be (I stress maybe) creating opportunities for ash encounters. However I don't see that the type of different flight profiles flown by D-CMET other than the one time event are being encouraged. This to me is where the authorities who have the resources should be deploying aircraft equipped with the type of equipment on D-CALM and D-CMET that can measure the particulate.
If for no other reason than this is a unique opportunity to create a lab to examine the situation for future occurrences - we should be encouraging science to get involved in this situation.
With that said - may I just hope that we can get a degree of qualification rather than conjecture into this process. My one nagging fear is that we are creating a situation of reducing life of an aircraft's engines that will result in premature failure - long after the equipment has lived its primary life in a well cared for home and gone to that lesser grade second cousin three times removed that you don't want to acknowledge and the EC occasionally blacklists.
Cheers