Hi MG,
Resetting the developer token every month doesn't give you any extra benefit from a security standpoint. The only situation in which it makes sense to reset a developer token is when it gets shared with someone, and you don't want to make the person making API calls using that token. On the other hand, resetting a developer token means that you have to redeploy your application with the new developer token (since the old token no longer works), and it becomes difficult for us to troubleshoot an issue you may have, since the issue might have happened a couple of months back, and tracking by token becomes difficult since you'd have reset the developer token couple of times by then. Developer token doesn't influence account ACLs.
You can reset the clientSecret as part of the security policy. When doing an offline flow, ClientSecret is the secret passphrase that proves to the authentication server that the client app is authorized to make a request on behalf of the user. See some discussion
here.
IMO the best way to enforce a password policy would be to require that your AdWords account's password is reset AND your refresh token is revoked at regular intervals.
Cheers,
Anash P. Oommen,
AdWords API Advisor.