Scale length (or the measurement from the nut to the saddle) has a big impact on the feel, response and sound of the guitar. A shorter scale length like Gibson's 24.75" will have a looser feel, producing a warmer, more mellow tone whereas a longer scale length like Fender's 25.5" scale length has a tighter response with a brighter, snappier sound. Of course, a shorter scale length means the frets are closer together, which can make fretting chords more comfortable. The additional tension of a longer scale length can create louder projection, something to consider if you're looking for the next 'banjo killer' dreadnought.
Nut width and bridge spacing really have to do with the physical comfort of the guitar more than impacting the sound of the instrument. As much as jumbo acoustics may feel cumbersome for smaller guitar players, you may consider a different nut width depending on the size of your hands. Players with large hands may prefer a wider nut width. A narrower a nut width means the strings are closer together, making intricate chord fingerings more challenging for larger hands but just right for players with smaller paws. Maybe you wrap your fretting hand thumb around the neck to fret the low E string, playing psychedelic RnB a la Jimi Hendrix or the thumbpicking style of Merle Travis? Both of these artists preferred a narrower nut width to facilitate their styles. Are you more of a fingerstyle player? You may find wider bridge spacing more comfortable for your picking hand.
While these suggestions may serve as a general guide, these guitar measurements are really about your personal preference. Pick up your favorite guitar and consider its scale length, nut width and bridge spacing. What about that guitar really appeals to you? Is it comfortable? Maybe there's something about it that you wish were different. Go to your local guitar shop and play some instruments while keeping in mind these various options. If the exact combination of features isn't available on a guitar in your local shop, it's very possible one can be custom made to suit your preferences. Many boutique acoustic guitar makers such as Santa Cruz Guitar Co, Lowden and Goodall offer different scale lengths, nut widths and bridge spacings as custom options on their instruments. Good luck and happy strumming!