Within tires of a particular construction type, I have not experienced a difference in speed between widths. IOW, if I have a 23mm, a 26mm, and a 28mm tire all of the same construction, I'm not any faster or slower with any of them, at least if the road is reasonably smooth. (A really rough road will favor a wider tire every time.)

A tire of heavy construction (Paselas, as an example) will pretty much always be slower than a tire of light "performance" construction regardless of width. For another example, 38mm Pacenti Pari-Motos are noticeably faster than the 25mm Paselas.

Of course, I'm not a time trialist. Most of my riding takes place at around 17 MPH. If you're going a lot faster, you should consider aerodynamics as well. I would never time trial on the Pari-Motos...

So considering the kind of riding I prefer (moderate, non-competitive speeds on a wide variety of road surfaces, and occasional moderate-to-fast club riding) wider tires make sense for me. Considering the kind of riding you do is your own problem.