There should be an option for notes that allows the user to master password protect any notes you want to keep secret. I know LastPass had this.
This would be nice for credentials too. For certain credentials, relying on a PIN code (or even leaving the device unlocked) may be unsuitable such as bank credentials, but at the same time having the convenience of lower security access on the device for other passwords is handy.
The option of a password reprompt for Secure Notes would certainly make them more secure.