ggal, My feeling is that much of european architechture, museums, historal artefacts will be there for a long long time for us to visit. I have visited most of western europe and must say that it has a long history and I will probably visit either end this year or next year (this time round - spain, portugal and the likes).
However, i find that in our own backyard like indo china, asean and certain parts of china, they are continuously being "raped" by tourism and development. Most places will change tremendous over the next 10 years or so. And if we don't visit them they will be gone for good.
For eg - the nomadic lifestyle of mongolia is already under threat and very soon it will be gone forever.
Just my thoughts but I guess each of us are at different stage of our lives and will have different perspective.