What are the most effective strategies for revitalizing declining or underutilized urban areas while preserving their cultural heritage and promoting economic growth and community well-being?
This question is very contextual to the culture of urban communities in each country. However, to date the most effective strategy is to work together with the parties. Educating the public and choosing the right leaders (formal or informal) will speed up the process of raising public awareness.
In Australia there has been a lot of work done on "place making" strategies, see for example Better Placed (nsw.gov.au) https://www.governmentarchitect.nsw.gov.au/policies/better-placed
also what are called street activation projects see
New Urbanism & the Activation of Main streets by Hames Sharley
there are a lot of local government projects out there if you google using "Street Activation". Of course, it should go without saying that these projects work best when the local community is on-board and involved in decision making from the start.
I would suggest that in order to revitalizing the urban areas, the most effective strategy would be to include major stakeholders in the decision making process. It has been observed that in most of the projects only limited or influential stakeholders and their points get the weightage in the policy formulation. Local residents and their opinions are generally got neglected. If local people, their views and comments start getting some place and importance from the planning phase to implementation phase. No doubt, the results will be more fruitful and sustainable.