Encourage immigration from poorer countries with younger workers.
Like another poster astutely put: create an underclass, and diminish their country's cultural heritage.
Really, do immigrants diminish a country's cultural heritage, or enrich it?
Freezing culture in stone sounds like a great idea for stagnation.
Woah woah woah. Careful there, this line of argument has been used in the past.
Ditto with a previous mention of immigration making the country "less Japanese", which has shades of certain groups making a certain country "less German".