Talking to people, making sure that they're healthy, connected, secure, and that they feel like they can express themselves is more expensive than drugging them and/or warehousing them, so I don't think that avoiding the depression diagnosis should reduce public spending or concern with the same sufferers, but raise it. I also assume that when the people who are now lumped together in depression diagnoses are dealt with with more precise approaches, there will always be places among those approaches where drugging and warehousing will be the best option.
Treating sadness with drugs is like how we try to cure poverty with teachers.