So, is the "new" always better than the "old"? This is almost like asking: "How much memory should I have?" As human beings, the reason why we survive is partly because we both remember and forget. The "remember" part is easy: We learn from the past, and build upon our experience. After all, civilization is mostly an accumulative process. The "forget" part is not as apparent but equally beneficial. Imagine if you have to make a decision and there are thousands of voices in your head from past generations and ancestors (not just your parents and spouse) telling you what you should or should not do. Or, if you can still feel vividly every little physical and mental pain you have since the day you were born. At some point, it is beneficial to be able to forget or at least to park part of our memory into storage. So, I would submit that whether a particular "heritage" item (building, landmark, etc) should be conserved or let go will depend very much on how much present AND future "value" (social-economic, cultural, environmental, geo-political, etc) the society is assigning to the said item in the bigger context of societal/human development and progress. As the words "heritage" and "value" are often defined subjectively if left unchecked, it is important that all stakeholders agree on the definitions and the decision-making criteria and process.
In closing, I would like to quote what the Chinese strategist Sun Zi said in 512 BC: "The wise leader will always think about benefit when he is in a risky situation, and risk when he is in a beneficial situation. Risk and Benefit are just like the Ying and the Yang; they come in pair and from within each other. They are not mutually exclusive and must be considered and balanced in the development and implementation of a strategy." I would suggest that the same principle applies equally well in 2006 AD when we talk about the 'good' and 'bad' of Global Competitiveness.