Most assuredly!! Not that "put on" smile directed AT the audience you see from a lot of performers. Just your own expression of enjoyment, even if it's just tapping your feet and nodding your head with the beat. Smiling and gesturing, however you do it, in acknowledgement of your appreciation of your band mates helps to motivate the crowd. If you are sombre, so are they... even if they like the tunes. Take it up a notch... enjoy!

Laugh and the world laughs with you... applies to more than attitude.