It is doubtless that we are experiencing a dilution of microdialects and accents, however this merely reflects the greater physical and social mobility of the population at large.
There are reams of papers showing that the physical and mental health of a population are important for economic growth, the better both are the more growth there will be.
The effect of this tardiness has been to put physical activity in reverse gear compared with population trends and advances in tobacco and alcohol control and diet.