Commenting here as both an engineer and a cyclist, the difference will be negligible with respect to wind resistance. The cross=sectional area of the handlebars is a minute proportion of the overall area of the bike and your body. Where there can be benefits in changing handlebars is to increase comfort and put you into a more efficient posture. As partly suggested already, try tinkering with your set up, e.g a new handlebar stem so you are reaching more forward and lower, slicker and smaller tyres, pair of cheap plastic toe-clips (you may be surpriesd what a difference they can make), or more expensive clipless pedals/shoes.