Conservative engine upgrades?

I have a 2002 Bonneville SLE with 50,000 miles on it. All stock parts. I would like to get a little more hp and or torque with minimal modifications to the engine. I need to keep my car looking and sounding conservative and business like for my job so a new exhaust might not work. I was thinking a K&N air filter, maybe better plugs and wires and a new chip if that is a possibility. Any advice?