>Stop the rot before it is too late...<
Well said wideford. I suspect the lack of archaeological investigation is due more to lack of funding than, as you say a, "... leave it all safe in the ground for folk in the future with better or less-invasive techniques." consideration. Lack of funding was certainly behind the decision to leave the remaining sections of the Mary Rose on the seabed rather than lift them - let's hope they're still there when funding does become available.
I've argued this before but we don't get to better techniques via some fanciful time machine, we get to them by building up information and skills in the here-and-now through hands-on investigation - and that applies to any field of human endeavour not just archaeology. We are where we are today because of the successes, failures and mistakes of our predecessors.
There is also another factor, leaving things untouched is not always the best way to preserve them. Without wanting to open an old can of worms again, invasive root action from the trees growing on East Kennet Long Barrow must be causing havoc to the interior; if something is not done to counter that damage <i>now</i> there might not be a barrow to investigate in a hundred years time.