Helmet Fire,
Agreed - NVG is great kit to stop you bumping into things - but only if you are trained to use it properly and within its limitations.
The Aw139 CFIT/CFIW examples you talk about (I can only think of 2 of them of the top of my head) are not necessarily ones where the kit would have helped. Synthetic vision doesn't see trees, and enhanced vision can't see through fog. If you are flying over water, neither is particularly going to help stop you descending into it.
When you look at what gizmos we have on board compared to what you would have had 20 years ago, there is no comparison, yet we still don't remove the human error element, we just displace it a bit.
I still say the best investment for flight safety is quality training. If crews can avoid poor decision-making, you will rarely need the fancy kit.