Another way to say "it never hurts"
How about "No harm in?"
- No harm in being a bit more serious.
- No harm in saying "Thank you."
- No harm in keeping an eye out for the perfect job.
I'm not sure if this what you mean by "little bit less strict context" but a more casual, sarcastic way to say the same thing would be "It wouldn't kill you to say thank you."
"It would be a good idea to"... Perhaps?
It would be a good idea to say "Thank you". It would be a good idea to keep an eye out for a new job.
etc.
This way, it seems constructive instead of bringing in the negative connotations of "hurt" or "harm".