The Apollo 12 astronauts were instructed to return parts of
Surveyor 3 for analysis to see how artificial materials held up
from long exposure to the lunar environment. Taking photos
would have been insufficient and they certainly did not have
the equipment or the on-site expertise to make a detail
determination.

Plus for the 1969 crew, Surveyor 3 was not some ancient
artifact, having landed on the Moon only 2.5 years earlier.
And they were not taking pieces of the lander back to Earth
for mere souvenirs. It was for science and the (eventually
long-delayed) plans for long-duration manned lunar bases.

A lot was learned from this exercise, which you can read here:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710008092_1971008092.pdf

Preserving historic space sites on the Moon and elsewhere is
something that has been discussed and considered, especially
with the Apollo landing areas.

They will likely be treated first as restricted archaeological
sites by future scientists and later turned into tourist zones
with appropriate protections. I hope similar consideration
will be given to the unmanned landers as well. I would love
to know what happened to some of the Soviet Luna probes
and if Surveyor 4 actually landed intact or crashed (radio
contact was abruptly lost just before its touchdown).

I also hope this extends to other probes throughout the
Sol system. I certainly want to know what happened to
all those poor failed Mars landers.

You may find this online article from the November/December
2004 issue of Archaeology magazine to be of high interest:

http://www.archaeology.org/0411/etc/space.html

In particular, these two quoted paragraphs from the article:

According to the vaguely worded United Nations Outer Space Treaty of 1967, what it terms "space junk" remains the property of the country that sent the craft or probe into space. But the treaty doesn't explicitly address protection of sites like Tranquility Base, and equating the remains of human exploration of the heavens with "space junk" leaves them vulnerable to scavengers. Another problem arises through other treaties that proclaim that land in space cannot be owned by any country or individual. This presents some interesting dilemmas for the aspiring manager of extraterrestrial cultural resources. If the U.S owns the archaeological remains of Apollo 11 but not the ground underneath it, how to protect the former without disturbing the latter? Does America own Neil Armstrong's famous first footprints on the Moon but not the lunar dust in which they were recorded? Surely those footprints are as important in the story of human development as those left by hominids at Laetoli, Tanzania. But unlike the Laetoli prints, which have survived for 3.5 million years encased in cementlike ash, those at Tranquility Base could be swept away with a casual brush of a space tourist's hand.

In what may be the first instance of funded space archaeology research, a team led by Beth O'Leary, a New Mexico State University archaeologist, is studying legal ownership of artifacts and structures in space, and how one might go about documenting and preserving them. O'Leary's group argues that even though the United States cannot, by treaty, own the land on which the lunar module Eagle's descent stage rests, U.S. federal preservation laws and regulations nonetheless apply to the objects left there. They see the base as a natural candidate for the National Register of Historic Places, as a National Historic Landmark, and, potentially, as the first extraterrestrial site on UNESCO's World Heritage List.