Kai,
On your suggestion of using another plane for a high current or noisy ground, rather than splitting a single groundplane - wouldn't that be counterproductive? If there are two parallel planes, I'd have thought that at high frequencies, the large capacitive coupling would make them perform as one. This would ruin the point of separating them, surely?
At least splitting a single plane minimizes inter-plane coupling.

Similarly, your suggestion of taking all external connections away from one point on the module conflicts with segregating noisy and sensitive interfaces. Perhaps it's a compromise that is quite difficult to resolve.
I will continue to place my load cell input and ADC at the opposite end of the module to the mains input and control I/O... But still worry ;-) What do you think?
Dave