Conflicts between subgoals indicate premature fixation on alternative solutions. The alternatives shouldn't be prioritized as goals in and of themselves. The other aspects of their evaluation would fit better as goals or subgoals to be optimized. A goal should give you guidance for choosing between alternatives.

In your example, one might ask what goal can one optimize to help make good decisions between policies like "replace old buildings with better ones" and "don't lose architectural masterpieces"?