Renovating isn't always the easiest solution. If often involves a lot more work, specially since you need to bring things up to today's code, and in many cases it would actually be most cost efficient to tear down and rebuild.
I have my own reservation against LEED (and I'm a LEED AP), it seems more of a marketing scheme than an movement towards green design. It would be a lot more effective to change our building code to incorporate more "green" building requirements.
Your questions taps into some fundamental questions about architecture. Buildings should be designed to stand the test of time, so they should be designed in a manner that they can easily be modified to future uses.
All in all I would argue its on a case by case basis.... more